I'll go with Saiyan for the Chi

If the kryptonians have the weaknesses and limitations of one, then no, not even worth it.

Green Martians is definitely worth it, but too op for my tastes, and there is that fire thing too.

Saiyans is more likely best option.

Viltrumites are boring, they are just all muscle.

^ it's the real world so kryptonite wouldn't even exist but even if it did kryptonite is a rare mineral in DC so it's unlikely you'd run into it alot and even if you did you'd just be as weak as a average human which we're already used to now, or just use super breath to blow it away.

But I agree with everything else you said although I'd go with Martian.