I definitely understand not wanting to get rid of characters, especially after investing the ISO, but in the grand scheme of things, you haven’t really put THAT much ISO into your 1-star characters. Higher-star characters are gonna suck up TONS of ISO by comparison. I actually built up a Juggernaut from scratch in under a week, just using Standard tokens, previously unearned Prologue mission rewards, and a chunk of ISO I had saved up combined with the daily Deadpool ISO.
I sold a fully-covered, fully-leveled 2 star character who was honestly pretty useful, just because I had a 3-star that I couldn’t bear to sell. I’ve had to sell a couple 3-star characters who I’d built up kinda far, because I knew they had very limited utility, and the characters waiting to be picked up would be very useful later on.
Transitioning from 1-star to 2-star is a lot easier (faster, and less painful) than going from 2-star to 3-star. If you’re already comfortable using your powerful characters, and you don’t use your 1-stars that much, it’s reasonable to start cutting them. It sucks, sure, but at least yours aren’t completely maxed out like mine were when I had to sell them. There are tons more 3-star characters than any other star level, so it’s easy to get carried away & miss out on strengthening a core of 2-star characters (I messed this up for myself bigtime). I’m not saying sell off your 3 & 4 star characters, but realize that a maxed-out 2-star is still very useful once you have a lot of 3 and 4 star characters. (a 2-star caps at level 94, but a basic 4-star is only level 70 & won’t have more than 1 castable ability)
The other thing to keep in mind is that there’s a lot of 1-star covers given out as rewards throughout the whole Prologue. If you haven’t gone past the Venom part, you’ve still got lots of covers as mission rewards heading your way. You can always regain a character you’ve sold, and it’s very easy to do with 1-stars. Between mission rewards and Standard tokens, you’ll be swimming in them.
Between Reed, Daken, and Torch, you’ve got match damage all accounted for, but you don’t really have many castable powers.
Based on who you listed as pending rewards (Captain America, Captain Marvel, Ares, and Thor),
Cut 1-Storm, add Thor & stack on however many covers you have waiting for him.
If you use your Black Widow for her stun ability (she could work with Torch & Reed in Daken’s place), it would make sense to hold onto her, but if you don’t use her at all, you may as well cut her too. Ares can get scary-strong, but Captain Marvel might be a good choice if you want another color, since Thor/Ares have the exact same colors. If you just can’t fit everybody, that’s okay. You’re gonna get a lot more of these same covers. Same is kinda true with the 3-stars. They’ll always come around again eventually, but just not as soon as the 2-stars. Make sure you save room for 2-star Black Widow (or at least, decide in advance who you’ll be willing to cut once she comes along). I went a long time without adding her, and I regret it. Even though she’s relatively low level, she can be really useful on a high-level team against certain opponents, as long as the other 2 on your team are strong enough to protect her.
Your 2-star Storm might seem useless right now since all she can do is counterattack, but she and 2-Star Magneto work very well together, and I recommend keeping the two of them & building them up over time to help you fight disproportionately strong opponents. Even if they don’t become your main focus, they’re very useful.
If you’re only at the Venom part of the Prologue and you haven’t done Oscorp or Dark Avengers chapters yet, then you’ve got some more Hero Points mission rewards to look forward to. There should be at least 100 HP in rewards, probably a bit more, if you haven’t gotten into those yet. You might not get them soon enough to save another character from expiring, but you’ll be able to make use of them soon enough.
Another thing I’ll say is that you shouldn’t automatically get rid of the 2-star versions of Daken and Human Torch if you come across them. Their abilities are basically the same as the 3s, but because 2-star versions develop faster, they’ll almost certainly outpace your 3-star versions.
I know it doesn’t help to talk about characters who aren’t part of the problem at hand, I just want to make sure you’re not making the same mistakes I made.