Unrostered characters on the vine, not enough roster spots

cooperbigdaddy

I'm in an awkward spot. I currently have all the 4s rostered! And I'm slowly but surely working my 5s up to usable. But here's where the awkward spot comes in- Roster Slots and characters I don't have rostered.

As of now, I have a guaranteed 1 spot open.

Here are the characters I have "dying on the vine" to roster:
5Venomsauras Rex (7 days)
3Jubilee (13 days)
5Kamala Khan (18 days- 4 days till I have to apply a Lockjaw 280 cover reward)
5Gwenom (18 days- same as above with 4Gwen)
I don't have 5May yet and I'm sure she will be required soon. (I will probably break my LL/CP till I get a cover when that happens, but that's another slot.)

I currently have 4425 HP and am hoping there will be another March Madness/Spring Cleaning vault with 4 slots soon! Otherwise, I feel like my only other option is several characters I could ascend but not for max rewards.

Thoughts??