I’d let the 5* aside for a moment and finish the 4*.
For purple: max Rigard, he’s on 4th tier and a very valuable healer. Then I’d max Proteus, he’s very helpful against all kinds of bosses, in raids etc. 
Cyprian might be helpful with his riposte - or Boril. Sabina is a good dispelling healer, too…
Yellow: Wu Kong is a must have against titans, but depending on the titan level it might be that 3/60 is enough for the moment. If not, max him. For purple titans, Jackal is very helpful, too. Li Xiu is a good choice, she can be a very good tank or flank. Chao is a nice sniper, but I’d rate him lower than Li Xiu (others see it the other way round). Hu Tao can be helpful sometimes, but he’s too slow.
Natur: Melendor should be maxed and his costume, I’d say. A very helpful healer with dispelling abilities like Sabina, but he’s very squishy. Buddy can make a good tank in some tournaments. Caedmon is a valuable sniper. So I’d max one of these three and give them priority. With your roster, I won’t max out Kashhrek, he’s a very good tank in lower levels, but you have other good tank options (Li Xiu, Boril). Gadeirus might be helpful. LJ and Skittles can be good in challenge events for bosses. I won’t bother with Gobbler, he’s overall meehhh.
Blue: Kiril is a dragon banner, but I think he’s good at 3/60 and I’d max out some others first I have 3 maxed Kirils for war and I don’t regret it. Then you have some tough choices. Snya is a good sniper and dispeller. Triton is a very good 4* sniper and he pairs well with healers. Grimm might be very useful with his def down. Boril might make a good tank. Agwe is more mehh, I have him maxed, but use him seldom now.
Red: For titans, Falcon and Wilbur is a must. Boldtusk, too, they make up a good red stack (Boldie, Wilbur, Falon, fired in this order). You won’t need Gormek with Tibs and Grimm. Scarlett has huge tile damage, Kelile is fast. Colen is good for bloody battle tournaments or rush attack.
In general I’d concentrate on at least 2 healers, but mix some snipers in, do this again for other healers/colors.
Not an easy choice then…
Def atm: Rigard, Jackal, Wilbur, Kiril, Jackal maybe? Wilbur is not the best on def, so I’d switch him out when you have something better.
Leveling order maybe:
Rigard => Proteus => Tiburtus => Sabina
Li Xiu => (Wu Kong) => Jackal => Chao
Caedmon => Melendor + C => Buddy => Gadeirus
Grimm => Triton => Sonya => Boril (or Boril first, if you want to use him as tank) - maybe Kiril to max somewhere in between
Wilbur => Boldtusk => Falcon => Scarlett => Kelile => Colen => Gormek
possible def then: Grimm, Caedmon, Wilbur, Li Xiu, Rigard…not ideal with Rigard in the corner, but hum…
You really have great heroes, but they won’t be maxed in a blink of an eye 
For Titans I’d take Wu Kong, a def down hero (if possible, according to color) OR Wilbur, maybe Kiril or Boldtusk and then appropriate colors.
I hope it’s not too confusing now -.-
