Hi, Chip -
Wet sand vs dry:
Dry sanding tends to fill, (clog,) the texture of the sandpaper with paint residue, soon rendering it ineffective for use.
Wet sanding keeps the paint residue floating away, the paper remains useful for much longer and stays fully effective. But the paper does eventually wear down and gets replaced.
It doesn't take much water, I mostly do it over the sink and keep a small plastic pail filled with water, then if the part is small enough to dunk in the pail as needed to rinse it works well, or I can rinse the sandpaper in the pail as needed.
I mostly use 600 grit wet or dry for the more agressive sanding, then smaller grit for a smoother surface finish, prior to spraying final paint layers.
PFC ; That's excactly the same label as on mine, I only use it for dipping canopies and other clear bits. For spraying a clear finish over paint, I use several of the model paint company clear coats, like Micro Scale Clear or Testor's, etc.
PFC, (for me,) seems to be a bit more fiddly, often results in a pebbly finish when sprayed, it does brush on very well though. Likely my limited expreience with it, others swear by it for spraying.
Build on, sounds like you and your son have some enjoyable times ahead.
Patrick