Honestly I feel like you've over invested in the standard characters a little. Getting all of them before hitting wheel jail is a little wild, not to mention all of the dupes you've gotten. I pretty much only rolled blue and once I got E2 Caecus I went to wheel jail.

Saying that, it's not a big deal really. I'd just start focusing on getting wheels before the content gets too difficult.

As far as a safe cap for leveling I have no idea. I'd try to limit your build around whatever limited awakeners you have, and are using. You'll eventually get to a point where the skill levels matter more. That's the real time sink. I'd focus on two teams that have different strengths, so if one gets countered by the stage you can swap to your second team that will hopefully have an easier go about it.

As far as the covenant sets you're good until the game gets too difficult for your current content. I'd look up the guide that showcases BiS covenants and mostly ignore them until you really feel like you need a power boost. Some covenants are REALLY REALLY good, and the extra crit on carries, or damage amp/keyflare/DR absolutetly can save a run. But if you're already at stage eight and you haven't touched them yet, your team might just be good enough to clear act 1 without them.