Man you have actually really good champs. Biggest mistake you are making is trying to level to many. Focus on 3 and get them to 60 and then the next two. Also get MM out of your reserve vault. 

MM is officially out of the reserve vault! I'm guessing he should be one of the three I should be focusing on? Should I go for Madame Serris or Keeyra next (I'm counting Ronda as one of the three)? Thank you for the response!

first off, stop trying to do every part of the game simultaneously. the only areas you should be focusing on at the moment are grinding 12-3
brutal to level food, dragon, clan boss, and classic arena. tag team arena is worth participating in just to start building up gold bars, but you're a long way from being able to climb the ranks. just set three garbage champs in your defense and hit anyone who does the same. as for hydra and nightmare campaign, forget them entirely.

in regard to champions, the biggest piece of advice i have for you is to stop putting resources into champions if you aren't intending to take them to 60. don't level them, don't ascend them, and certainly don't awaken them. 

as for who to keep and who to get rid of, you'll want to hang on to every champion of epic or legendary rarity. for rare champions, you should hold on to a copy of every champ that can be used in a fusion (marked with the swirly blue symbol on the bottom next to their level). elhain and kael are also worth keeping with the resources you've put into them, although i wouldn't bother taking them up to 60, and both renegade and frozen banshee are worth hanging on to. beyond that, everyone looks like food to me.

assuming your ronda can run 12-3 solo (if not, you'll want to either rebuild her such that she can or rank up someone to do that) your next 60 should be deacon, and i'd suggest toragi after him.

Yeah, I figured I was focusing too much at once. It's bit me in more than one game. I want to do everything! I was already working towards Toragi and adding Deacon makes sense. Many thanks!

In terms of rares worth keeping: https://plarium.com/forum/en/comment/topic_1633283/

Specifically, I'd recommend holding on to Master Butcher and Metalshaper, at very least. They may prove essential for your doom tower boss teams.

Yeah keep farming campaign and burn your self out of the game lol.  Working on videos to help support this theory and produce vault tips, lower player power level and build champs if someone does farm a lot in Campaign. My vaults are full as well and it's hurt my F2P accounts. Check out the channel under same name here. thanks 

Ignore that advice. Power level is irrelevant. Don't waste time leveling random champs, but don't stop leveling the ones you need.

Thanks, everyone! I think I'm making progress. At the very least, I know I have a few champs who are better than I thought they would be! Glad I didn't feed them to one of the bad heroes. I'll check out your channel, Chief!