If you’re looking for immediate rainbow progress then
Purp - Proteus - abandon everything, proteus is your best hero. Cyp can keep waiting. Proteus number 1. I’d actually feed him your red feeders too because gormek is pretty meh.
Red - you can bring gormek to 3/60 while you wait for a better red imo. But i think I’d give your red feeders to proteus because he’s way more useful than the hungry one will ever be
Yellow - wu. I use him for everything, atk def and titans, although he’s defs not the best on defence. He’ll make a huge difference on your titan scores and offense so easy choice over chao.
Definitely caedmon for greens. Some people think kash is a decent tank (i disagree - he was my fave tank to come up against in low-mid plat), but you’ve already got bt maxed so you don’t need him. Gad is really only good in buff booster tourneys so he can wait too.
Blue - you’ve got a lot of good options here so it’s going to come down to your playstyle preference/goals ultimately.
Want a second heal/buff? Kiril
Extra debuff to deal with rampant riposte in gold/plat? Sonya
Want to get some extra oomph from bt and still have a sniper? Triton
For my playstyle i think I’d recommend grimm>sonya>kiril 3/60>triton. Kiril works fine for me at 3/60 when his skill is maxed, i find I don’t need his extra atk. Grimm is useful on offense with the def debuff and high atk, and will help on titans a lot more than gormek. Sonya’s great on offense and defense but i think having a def debuff is a little more useful since you’ll have caed already. Not a kiril fan at all myself, but like i said before his skill can be useful at times. Triton is a really good sniper but not very versatile beyond that. edit family bonus with Triton/proteus is nothing to ignore either. Really helps keep proteus alive to get off his special, which is absolutely game changing.
Hope this helps. Cheers