Let the nail polish dry sufficiently. To veer on the side of caution, let it dry for a few days. If its too sticky, take some nail polishing files and gently file off a bit of nail polish.
As to the second part... I don't know, as mine isn't here yet... Perhaps you mistransformed it?
I think your right on the second part. When I transformed it again, this time it didn't bulge, it was flat.
Was your hip joint loose when you took out your YF-21 when it was still new? When I transformed my YF-21 for the first time, it was so I took apart the hip joint and wrapped some scotch tape on the ball part of the joint. After I put back the hip section together and tested it, It wasn't as loose as before. It was a little bit tight, but still a tad bit loose. Should I add some more scotch tape to tighten it up? By the way, this particular valkyrie toy sure is hard to pose! You had to go through a balancing act before you can make it pose perfectly.