Been awhile since I’ve helped out with one of these, so I may be a little rusty, but I’ll give it a go:
Alright, so solid advice above. You’ll definitely want to focus on your 4* first, as they’ll be stronger than your 5* until your 5* hit 4T, and I doubt you have enough mats to take any all the way yet anyway. Also, they’re quicker and cheaper to level than 5*, and take half as many mats. So, I wouldn’t be working on any 5* heroes until either you 1. Run out of solid heroes to work on in that color 2. You have all or most of the mats to take them to 80 3. They’re extremely good heroes, with uniquely helpful specials, that would be of use at 60 or 70.
Also, I’d stick to on-color feedings, building up a rainbow team of 4* one after the other, as there’s a 20% exp bonus with on-color meaning you’ll get more heroes leveled in the long-run.
I prefer variety over dupes, so I’d always level a unique hero when you’ve got one. However, certain dupes come in handy, like the heroes with versatile specials (healing, buffs, defense downs, etc), so I’d hold onto them while you’re filling out your roster for war. If it comes to it, purchasing roster space is fairly cheap, and a much better option than feeding away a hero that could be difficult for you to obtain again.
Also, I’d be keeping one of every solid 3* for events and war. I’ll list them below, and would recommend working on them after you’ve completed a few teams of 4* first. They’re super fast and cheap, and you’ll need them if you’d like to participate in all of the Weekly Raid Challenges as well.
First, I have to say it is usually much easier for someone to give assistance with an actual photo of your roster, as it helps us to visualize who you have without having to read through a list. As you’ll want to do one hero of each color at a time, at the very least, grouping by color would help a ton. So, this may be a little more difficult for me to spot what heroes should go where, but I’ll give it a try. Just for future reference, but I’ll make it work 
Red: Boldtusk is an amazing hero, makes an excellent tank, and has a solid attack buff that’s amazing for titans and raids. Plus, you’ll need several healers for war, so I’d focus on him first. Next, I’d do Scarlett for that crazy high attack stat; she’ll work amazingly against green titans and in a red stack. Super squishy though, so belongs in the wings on defense. After her, I’d do your second Boldtusk unless you happen to get any other unique red 4* first. (4*)
Nashgar, Hawkmoon, Azar, Rudolph, Namahage, Squire Wabbit (3*)
Anzogh can wait. He’s an alright hero, and your only red 5*, but will be much weaker than your 4* until he hits 4T. So I’d be waiting to level him til last, and only take him to 60, or 70, and play around with him first before deciding to spend 4* mats on him. He may work for you, but it’s best to be sure before using those mats, as they’re extremely rare and difficult to obtain. He works well in a red stack, but isn’t the most spectacular hero. Still has his uses, but again, best to see if he works with what you’re looking for first (5*).
Blue: Grimm first for sure; he’s the best of the pulverizers, so he’ll be of use in nearly every aspect of the game- especially vs Titans. Next, I’d do Kiril for that buff and heal (they’re amazing). Third, I’d do Sonya for that fast hit and dispel; dispel is an important tool to have at your disposal. Do Boril last (4*).
Valen, Ulmer, Gato, Gunnar (3*)
Both Ariel and Magni are top-tier 5* heroes, that both definitely deserve 4* mats when the time comes. Magni is an amazing fast sniper with an incredibly high attack stat and a great defense buff, and Ariel is one of the only average speed 5* all allies healers. Ariel also cleanses all allies, with a mana gen boost, so like a super charged Rigard. As she’s not dependent on being at 80 for her SS to be the most useful, she’d be a good candidate for going to 60 or 70 early because of that heal, cleanse and buff. So I’d actually start her after Sonya, maybe even after Kiril if you find yourself having enough dispellers at your disposal. As for Magni, I’d wait to work on him a little longer, as he really needs to be at 80 to excel, but would still probably put him before Boril, as I’m not a huge fan of his (5*)
Green: I’d do Jack O’Hare first for that incredible attack stat and fast special for some firepower, so will be great against blue titans and in a green stack. Then, I’d do Melendor for that deep heal and dispel, since both are handy. Although, he is pretty squishy, so not the best of the healers, but that attack stat works well when you need the tile damage. After, I’d do Kashhrek if you decide you want a better tank than Boldtusk, or if you need more healers, but if neither are necessary, then I’d hold off on him for a bit. Instead, I’d do Little John for that attack stat again; he can be extremely destructive if he goes off. Then, I’d do Kash if you haven’t already. Skittleskull last. Wouldn’t bother with the Kash dupe for awhile unless you’re desperate for healers (4*).
Belith, Brienne, Berden, Mnesseus, Hisan (3*)
Yellow: Definitely do Wu Kong first for that tile buff; he’s one of the most crucial heroes for titans if you want to score well. That tile buff is insane, but not as great in raids unless you’re against someone you’re much weaker than, giving you an edge if he pulls through. After, I’d do Chao for a fast mana cut; mana control is extremely important to have, and he looks to be your only one at this time. Hu Tao last (4*)
Bane, Gan Ju, Melia, Kailani (3*)
Purple: I’d do Rigard first for that cleanse, as he’s the only 4* with that SS, and has an amazing heal. I regularly run two healers, so this could work to your advantage while you’re just starting out. After, I’d do Tiburtus for another pulverizer, as he’ll be great vs holy titans and in a purple stack. After, I’d do Sabina for another healer and dispeller; she’s squishy like Melendor, but another great attack stat. Cyprian last (4*)
Balthazar, Tyrum, Chochin, Gill-Ra (3*)
Hope this helps; feel free to ask anymore questions if you have any 
