I haven’t read every comment, so I apologize if I repeat anything that’s already been said, but it’s been awhile since I’ve helped with leveling so I’m just gonna go about it as I usually do. Thanks for tagging me so I could see this and [hopefully] help, or at least reaffirm what you’re already thinking 
First and foremost, I want to suggest doing on-color feedings if you haven’t already; the 20% exp bonus is pretty huge.
Also, I would only work on one hero in each color at a time until they’re either 1. Maxed or 2. At the mat wall. You don’t wanna work on too many heroes at a time, spreading your feeders to several mouths at once, because it slows your progress down significantly. Also, taking a hero to max, on whatever ascension they’re on, ensures their stats are the highest they can be ie they’re at their best for offensive and defensive purposes.
I’d continue with leveling like you’ve been doing: getting a few 3* maxed in each color for the beginner tier of challenge events, but mostly prioritizing 4* til they’re at max. 4* will be your backbone, so I’d always be leveling them first, then 3*, then 5*. 5* I wouldn’t even bother starting on until you have enough heroes leveled in each class, in each color, and are close enough to having all of the necessary mats to take them to 80 (or at least 70). 5* hold up your roster progress quite a bit, with their time and resource consuming leveling process, so I’d always wait to take these kinds of heroes to max until you’re satisfied with your roster depth for trials, events, war, titans and raids. You can take four 4* to 3/60 in the time it takes to max one 5*, so definitely prioritize your important 4* first.
Another thing, I see a lot of dupes. I would keep at least one copy of all of the good 3* and every unique 4* and 5* that you pull, and two to four dupes of the really amazing cards. Depending on how many pulls you do, you could get away with only keeping one dupe of the good regular 4*; chances are, you’ll pull them several times before you get an opportunity to level that dupe. However, if you don’t do many pulls, it’s always better to be safe than sorry. Expanding roster space is fairly cheap, and one of the best investments in this game, so if you’re ever unsure about eating someone- better to expand your space and think on it first.
With leveling dupes, I would always prioritize variety over dupes, at least until you have all of the necessary bases covered (healing, buffs, dispels, etc). Eventually, you’ll run out of good heroes to work on in that color, and at that time I’d start with leveling dupes. Healers are some of the best dupes to keep (always need healers for war), as well as defense down, dispel, buff and cleanse. I won’t be listing when you should level your dupes, but you can basically do it when there’s no other solid options to work on.
As for the trials, I’d suggest getting three or more heroes in each class to at least level 60, but preferrably maxed- to ensure you’re able to complete every stage of each trial. If you’re lacking in a certain class, have that take priority over certain heroes if they’re the non-essential ones. I’ll list the important heroes first, but let you decide on who to level afterward based on your need in a certain class.
Now, for leveling:
Red: You already have Wilbur maxed for the spirit link and defense down, and Scarlett for her high tile damage, so I’d suggest getting Colen to 60 (I mean, he’s at 59- so might as well), then getting Kelile there as well since she’s already 2T. The next hero I’d use mats on would be Gormek to have another pulverizer leveled. After Gormek, Colen for defensive purposes, or Kelile for another fast sniper. Depending on if you’re lacking in a certain class, should make deciding between Kelile and Colen a little easier. Even Gormek isn’t super essential with Wilbur in the picture, so I’d decide who to max after they’re all at 60, depending on classes. Though, if you happen to pull Boldtusk, I’d make sure to level him asap. He’s an essential hero to have maxed (4*). You’ve already got quite a few 3* maxed, but I’ll list the important ones just in case: Nashgar, Hawkmoon, Azar, Namahage, Rudolph (3*).
Blue: Kiril is maxed for his heal and dragon banner, so that’s awesome, and Sonya is already at 3/60 for her dispel. Honestly, I would max Sonya next [out of your options]. If you happen to pull Grimm and/or Triton, I would get them in the works asap (and they deserve mats as well) (4*). While you’re waiting on mats, I’d get the good 3* maxed: Valen, Ulmer, Gunnar, Karil and Gato (3*). Out of your 5* blue options, Richard is the best of the two, but both aren’t overly amazing. Still, if you want to ascend one of them, I’d do Richard. However, I’d get Thorne leveled to 60 since he’s already almost there, but leave him there indefinitely, or for whenever you have an excess of 3* mats and can safely take him to 70 [without wasting necessary mats] (5*).
Green: You already have Caedmon maxed for the dispel, so that’s good. Next one up to max would be Melendor for his deep heal and dispel. After, if you have no other options, I spose Skittles to have a sorcerer leveled- decent tile damage at least. If you happen to pull Little John, I’d level him for his high attack stat. Also, Gadeirus for the attack buff in green for blue titans. Kashhrek if you want the best 4* tank for war and defensive purposes (4*). Important 3*: Berden, Belith, Brienne, Mnesseus then might as well do Carver to have a fifth green 3* leveled (since he’s already at 3T anyway); the mana cut could be valuable. Although, Carver isn’t too amazing, but still nice to have five heroes in each color leveled for a stack during events (3*).
Yellow: Awesome, Wu Kong is maxed for that tile buff, which always helps immensely with titans. Li Xiu is also maxed for the mana cut on all. Next one I’d work on would be Chao for a faster mana cut on one. I’d max him next when you can, or else at least take to 60 for the time being. Hu Tao isn’t too great, so I’d leave him til last unless you really need another fighter (4*). Important 3*: Bane, Gan Ju, Kailani, Melia and I spose keep Dawa as the fifth since she’s already maxed (3*). Justice is a beast of a tank, but not too great offensively, so I wouldn’t be in a rush to max her. I’d hold her off from going to 70 until all of your important yellow 4* are leveled (so basically just Chao). Idk if I’d take her to 80 though; you’d have to decide for yourself if she’s worth it. If you want a tank, then she’ll be great for that. Otherwise, I’d wait (5*).
Purple: Rigard is already maxed for that deep heal and cleanse, which is important. Next, you might as well finish Cyprian since he’s already 4T. After, I’d get Tiburtus in the works asap for defense down in purple; always important to have all of the pulverizers maxed. He’d be the next one I’d give mats to. After, I’d do Ameonna for her high tile damage; pretty niche, but great against yellow titans. Plus, she’s a sorcerer. If you happen to pull Sabina, I’d get her leveled as well for another deep heal and dispel; she’s also a sorcerer, and those are fairly lacking in most rosters (4*). Important 3*: Balthazar, Tyrum, Chochin, and Gill-Ra, and might as well use Oberon for the fifth since he’s already maxed (3*). Domitia is pretty amazing solely because she’s the only dispeller out of the regular, season one 5*. I think she’s worth going to at least 70 after your 4* are done. I’d consider 80 if she fits with what you’re looking for. I do like her the most out of your 5* options (personally) (5*).
Now, looking at your mat inventory, I would still definitely work on the 4* I list above and get them maxed first. I see you do have enough mats to max a few 5*, however I’d suggest holding off until you’re satisfied with your bench depth for trials and war. If you don’t do many pulls, or run many TC20s, I’d go ahead and max the best 5* you have in that color (I’ve listed them above). If you’re unsure though, I’d wait and think on it. Take them to 70 and play with them for a bit before spending those hard-earned 4* mats. They’re super rare, so I’d be sure before taking that next step.
Honestly though, if you do plan on making pulls during Riddles and Atlantis, I’d wait on maxing any of your 5*. If you’re super anxious about maxing some of them, take them to 70 early and see if you like them. That will also give you time to see what other heroes you may pull.
With defense, I’d suggest doing rainbow to deter people from stacking against you. Never ever double whatever color your tank is anywhere else in your lineup. If you have to double colors, separate them to opposite sides. Never put two healers right next to each other; it makes it much easier for the opponent to throw dead tiles their way. Also, always keep heroes that buff their neighbors in flank or tank position. Al moves from left to right, so always have dispels, cleanses, attack up and defense downs on the left.
The best tanks are the heroes with high defense/health stats, that either hit fast and hard, slow the opponent down, or support their flanks enough to do the same.
Flank is where you’ll want your important heroes, like mana controllers or defense downs, to ensure they’re protected by the tank, but also giving them sufficient enough chances to charge and wreak havoc.
In the wings, very fast or fast mana heroes work best, since they don’t need much to charge. Also, it protects heroes like Scarlett, who are glass-cannons, and helps them survive a little longer. Snipers work pretty great here.
Rainbow Defense Team (With the Heroes You Have Leveled):
Caedmon-Kiril-Li Xiu-Cyprian-Scarlett
Fast dispel [to remove any counterattack or defense buffs] first. Kiril to buff attack and defense next. Li Xiu to tank and cut your opponent’s mana, which then slows them down. Cyprian to put up riposte on that side. Scarlett to hit fast and hard.
Okay, so that was a lot of words, but hopefully it helps. This advice is all based on hero usability first, since that ultimately is the most important factor when considering who to level next. However, you should always keep in mind whichever class your hero is in, and which classes you’re lacking in. If you only have one hero maxed/leveled in a certain class, I’d prioritize getting a second and third before working on specific helpful heroes. Though, I would always choose the most useful hero in that particular class to level; the one you’re most likely to use elsewhere, not just in the trials. If you’re not really lacking in any certain class, then I would safely follow the above. So just remember to keep in mind the classes you may need: get 3 leveled/maxed per class.
If you have anymore questions, or would like help with anything else, please let me know. Or else happy leveling and good luck 
