Alrighty,
So my suggestion would be to run:
Li Xiu → Tiburtus → Kiril → Colen → Caedmon
I would work on getting Li Xiu & Caedmon up to final ascension.
Kiril is an OK tank. A better one would probably be Boril BUT Grimm is probably more useful overall (not for defence tho).
My suggestions for levelling:
In general, I would advise leaving 5* heroes be until you have more depth… a 5* at 3-70 is generally worse than a maxed 4* hero. A 5* at 2-60 is even worse… If you don’t have the mats to finish a 4* hero yet, I would keep working on more 4* to 3-60 or go back & work on some more 3* heroes.
Finish your 5* heroes you’re currently working on to the end of their current tier but no further after that… (Domitia to 3-60, khagan to 3-70).
Red - Finish Scarlett (if you have the mats) otherwise keep working on Sumitomo. Then go back & work on some 3* heroes until you get the mats to finish heroes off.
Blue - Boril or Grimm. Boril is a good tank & does OK in offence. Grimm is the inverse… does great on offence & against titans but isn’t the best on defence. I would personally prioritise Grimm over Boril for overall versatility but will be your call in the end.
Green - Caedmon & then Mel. I wouldn’t bother with Kasshrek until much later… Yes hes a good tank but thats really his ONLY use… by ascending him you will hamstring yourself for a while in terms of using rare ascension materials.
Yellow - Finish Li Xiu. No competition. After her I would probably advise Wu Kong & use him on all titans. He will bump up your attack (refer to link below regarding Wu Kong & titan damage buffing). Jackal would be next after that
Purple - Rigard next, no contest. Then go back & do some more 3* heroes.
Wu Kong & Titan Damage Boosting: