You’ve received some very valuable advice above. 4* are the backbone of E&P. Max out at least 3-4 rainbow teams of your 4* before even bothering with the 5*. You can max close to 3-4* with the AM’s/feeders/time it would take for you to finish 1-5*
I’d also suggest to not neglect your 3*. They are quick and require no unfarmable AM’s. They are also needed in tournaments/ event challenges.
I made the huge mistake of summoning and trying to level 5*’s when I 1st started and wasted a large amount of material and time for little return.
Your 4* will give you much needed choice when attacking in wars/raids/events. Those 5* will still patiently waiting for their time. But right now finish off your 4*.
Rigard, Kiril and BT should be your priority heros. They have a VERY long shelf life and will see you well into Diamond in Raiding. Then Proteus, he’s indispensable in helping you finish many of the challenge events and probably one of the best 4* to have overall. (Try for Wilbur too, those 2 Atlantis hero’s are GREAT)
You’ll want to also finish Grimm, Buddy, Gade, Melendor(somehow missed him so I’d bump him in with the healers at the top), Valeria (much underrated hero IMO, Caedmon and Chao. While Cyprian is useful I wouldn’t prioritize him as you’ll find he’s quite like Kash in the length of his usefulness. He’s also overshadowed by Boril. That said, since you have him almost finished he’s worth having for Trials and AW’s too. So it depends on your depth in ascension materials.
While Kash is probably the best 4* tank I’d suggest holding off on him as his usefulness is very short, although still useful in AW.