Alright, with leveling, I would actually prioritize getting a full rainbow team put together first. Although, Proteus is a game-changer, so I spose for now I could see omitting yellow. Eventually though, you should get Li Xiu (or even more preferred, Wu) leveled as your holy hero. Also, I would look into leveling Grimm to replace Kiril, and Boldtusk to replace Gormek. Grimm is a better pulverizer, and Boldtusk makes an excellent tank and he buffs attack and heals. Kiril is awesome, but doesn’t excel as much as Boldtusk on defense.
Red: I’d get Gormek to 60, then Boldtusk to 70. If you have enough mats to ascend Gormek after BT, then I’d go ahead. Although, if you make any pulls during Atlantis and nab Wilbur, I’d put him ahead of Gormek. He’s a much better defense down hero than Gormek, though it is always nice having all of them eventually maxed.
Blue: Finish Kiril to 70, then definitely get Grimm up and running.
Green: Finish Evelyn to 60, but then I’d work on Gadeirus to have more green heroes. Evelyn works best with a few other greens, so he will help with that. Plus, he’s awesome for blue Titans.
Yellow: Li Xiu for defensive purposes mostly, but the mana cut is nice. Hu Tao last.
Purple: Rigard is maxed, that’s good. Definitely Proteus next for the mana block, it’s amazing. Ameonna can be nice for yellow titans, so worth considering leveling if you don’t get any other purple options by then. Although, I’d put Tiburtus before her, Sabina too.
If you’re not leveling/ascending rainbow specific, and don’t care about running a rainbow team (which I do, but that’s your call), then I’d level Proteus first, then Grimm, then Boldtusk (since these are the best 4* heroes in your roster). After that, it’s really your call.
I’d probably do Gadeirus before Evelyn because his stats will be better, he’ll be cheaper, and he’ll be leveled much faster. That way, when it’s Evelyn’s time, she won’t be all alone in the green category. & I’d do Li Xiu if you don’t get any other yellow options, because you have absolutely no yellows, and it’s always best to have a few heroes in each color leveled/maxed. It’s nice to have all of the pulverizers leveled, but Gormek is probably the least important of the three, and I value BT way more. Especially if you make pulls during Atlantis, Wilbur will fill that role much, much better. Gormek is still worth eventually maxing, but not ahead of Proteus, Grimm or Boldtusk, especially if you’re short on the mats.
Eventual Defense Team:
Full Rainbow (Preferred):
Evelyn-Grimm-Boldtusk-Proteus-Li Xiu
I prefer fast in the wings, but not enough fasts to choose from. The most important heroes, that you for sure want going off, should be flank (especially since they’re usually average mana) to ensure their mana gets charged. Honestly, your best tank option is Boldtusk due to his beefy defense and health stats and his incredible attack buff, but Li Xiu could also tank well for you. You could also try Gadeirus there too, although I haven’t had much experience with him to know exactly how well he fits that role.
The team you have now, how I’d arrange it (out of the five you listed):
Kiril-Proteus-Gormek-Rigard-Evelyn
I don’t like having Kiril in the wings, but I don’t see anyway around that with two healers on the team. You definitely don’t want both healers on the same side, nor do you want the same color next to each other either. Typically, I’d want Evelyn on the left to dispel first, but the attack buff might be more critical. Same with Rigard’s cleanse, better on the left, but no way around that [that I can see]. Just always remember, Al moves from left to right, so you want attack buffs, defense downs, dispels and cleanses on the left.
Hope this helps, feel free to ask anymore questions you may have. Good luck 
(but anyone feel free to post, if you got some thoughts). Thanks Pandah, much appreciated.