If you let the epoxy dry for at least a day it sands fantastic but if you get on it too soon it will gum the paper. There is a 7 day re-coat window so no problem there. Also, you can apply filler over it without sanding first and it adheres great and feathers into the epoxy. You can also reduce the epoxy and use it as a sealer before you shoot your base.
Universal clear has a well earned reputation as a go to clear for restoration work.
And the prices speak for themselves.