I would use a more sophisticated keyer than color key. ex. Keylight, Ultimatte, Primatte. For a poor key, use garbage mattes too.(motion tracked rough masks)
You’ll be using multiple keys. Some on the torso, others for hair, hands, etc.
The best deflicker plugin I’ve seen is Tinderbox 1 deflicker, but if you have a flickering actor, you’ll need to fix that anyway.
AE has a few deflicker ways too, but not as tweakable as Tinderbox. There’s Auto levels(which I like), and color stabilizer. Another option if you have a pc is,
“a virtualdub plugin processes frames by parts in case of irregular flicker”
https://compression.ru/video/deflicker/index_en.html
You could even roto the flicker out if you really had to, but that would be a lot of work.
As for the greenscreen spill, some keyers simply do a small color correction, like AE’s spill suppressor. It’s like a secondary color ranger just for desaturating a certain color. You’ll want to use matte chokers/masks first so you don’t re-color the whole image. And finally, roto may be your only friend.
Good Luck.
https://technicolorsoftware.hostzi.com/