What a fun discussion!
I’m not as enamored with IM40 as Dormammu is, but I agree completely with him on 3-star Cap. His powers do require a lot of AP, but once you’ve built them up, he does a heck of a lot of damage on red, and unless the board is just cruel to you and you lose his countdown tile, you will be throwing that shield again very quickly, Cap is fantastic on wave nodes, where you’ve got time to use and reuse his shield.
I’m also not as enamored with Patch as DAZ is, but you’ll find him very useful in the right circumstances. On most goon nodes - NOT symbiotes, though! - his unusual power that gives your enemies strike tiles will not factor into things. He self-heals better and more efficiently than 2* or 4* Wolverine. He’s easier to keep leveling because the champed 2* Wolverine gives him covers, and, in turn, champed Patch gives you 4* Wolverine covers. (You’ll be getting 4* Wolverine very soon if not already. Three of his covers are the daily SHIELD rewards for days 149 and up to 180.)
Finally, a contrary note on Bonus Heroes: Since you’re beginning with 3s, I agree completely that you should pick one favorite 3. Every time you get a 3* from a Standard Token, you’ll get that Bonus. 5% of your 3*s from Elite and Heroic will also give you that Bonus. You should pick your favorite, and you will see that character appear very frequently.
But with the 4* characters, actually, I’m quite happy with having eight or nine favorited. I do not currently have any 4s champed - the closest I have come is Mockingbird, with ten covers - and so I’m perfectly pleased just to have the opportunity for any of these characters to get another cover. It’s more important to me right now to have several 4 characters around level 78-106, with three or four covers apiece, than a whole mess of them with a single cover at level 70 and just Mockingbird champed.
If your goal is specifically something like “I want 4* Medusa champed as quickly as possible,” then sure, favorite her and her alone. If you’re still looking for just more 4*s, period, and a broader base of characters, don’t spare the gold hearts!