1. probably . Usually better adhesion and more uniform results .

2. Yes . Static scale models enjoy an easy life .

3. No sanding needed unless you need to address areas that needed putty . ( or general removal of seam lines etc )

4. Up to you . Wet sanding is more efficient but not necessary .

5. No

6. No

Good rattle-can primer for polystyrene kits is the lacquer based Tamiya Surface Primer .

Or  , good adhesion from Rustoleum  Painters Touch ( 2X ) , which are enamels ( alkyd ) formulated for plastics as well as other surfaces . ( just remove and clean the spray nozzle with turpentine or mineral spirits immediately after each use or you wont be using that spray nozzle ever again .

Lacquer , automotive primers from various makers .