Alumilite Water Clear is what is recommended for headlights and Amazing Clear Cast Plus is specifically for non-yellowing BUT be aware, it takes longer for the Plus to cure and I'm not sure how it holds up on solvents.
I have a sun catcher that I made with the Plus somewhere around December or January and it hasn't had the slightest hint of yellowing. It hangs on the window that gets the morning sun as it peeks over the trees and on the outside of the shade so it gets full sun even when the shades are down.
Acetone will "melt" a lot of things, mostly anything that is any kind of plastic and acrylic is a type of plastic. Good thing is as long as you don't accidentally deform it, the acetone will evaporate off eventually and it will harden back up.
As for painting over any of the resins, you will need a "primer coat" and you can get that two ways. Paint it immediately after demolding while the casting is still warm - this is a little tricky but can be done. Or paint the mold cavity, let it dry, then pour the resin in - this is what I usually recommend as it's easier and the paint bonds better with the resin while the resin is curing.