But alas, I think I have narrowed down my keep list to; Ace DX, Brotherhood, WCF SW Suits, WCF Volume 4
Believe it or not (not to advocate selling everything) but over time you won't miss them as much. I've parted with a few rarer POPs and I don't really miss them. They weren't my favorites, and there's so many other figures I have that I just kind of forget. I think it also helps if you sell it because you want to, not because you have to. Having owned it you get to enjoy it, and after you sell it, you can still remember it for what it was.
I think your choices are great!! SDX ace is an amazing sculpt, as is brotherhood. WCFs are hard to let go as well, and the early ones were really great quality <3