I have been playing for about a month now, and have been enjoying it so far. But I am hitting a bit of a wall, and wanted to solicit some tips from the vets.

- I have 100% Act 2 and 96% of act 3. (Last quest of 3 is 0%, and only one not 100%.) Currently not strong enough to continue.
- I am working on the Heroic level of the current event, but it's tough! Finally 100% the Heimdall quest after buying a lot of heals. Kind of dreading the ramp-up on the next one.
- I have no 4* and have only maxed a few 3*.
- My go-to team right now is 3* Nebula, 3* Gamora, 3* Ant-Man, 2* Drax, 2* Rocket. All maxed. Drax and Rocket are strictly for friend buffs. All but Nebula are awakened, but few levels on the abilities.
- I haven't done any Vs, nor am I in an alliance.
- I refuse to microtransact. I will grind as necessary.
Is it worthwhile to grind old quests I have already 100%? I need gold, pretty bad. Lol. Should I drop units on crystals for that off-chance for a 4*? (I don't have much.)
Any tips on where to concentrate next would be appreciated.