While I haven't yet worked with vinyl kits I do have a few in my stash.
I would suggest picking up David Fishers DVD(s) since they not only cover resin garage kit's but also vinyl.
Items mentioned.
1, Heat with blow dryer to soften for cutting, use a fresh exacto and be very careful and take your time.
2. Glue together using CA glue (super glue)
3. Use lacquer based primer misted on.
4. Unless fully sealed don't use enamel paint as it will never cure
5. kit's can be filled with 2 part expanding foam, plaster or paper to help keep their shape.
6. Wire framing and 2 part epoxy putty (Magic Sculpt, Aves) can be used to modify the figure.