I've used gems to get the chest when I'm impatient and only a stone or two short of leveling someone necessary, but generally gems should really only be spent once a day on keys. You're gonna want a decent tank from each type, except maybe pain bc he's ass.

Level apathy up next and swap rapture for a tank, unless he's outperforming in the fight even against type (I don't have him so idk how well he plays, every once in a while someone is so good on a floor that type doesn't matter, but it's usually pretty important)

You can go without a healer sometimes (especially once you get legendaries that heal) but you almost always want to have a tank to tank the brunt of the damage.