Can I paint without sanding

Depends on what primer you use (if you use primer).  Many primers are quite flat. If you are using a matt final finish, a matt primer is okay.  However, if you need a gloss finish, it is probably better to sand the primer than sanding the first color coats- you will have to sand at some point in order to get a decent gloss.  Gloss color paint will not cover a matt primer to give a good gloss.

If you don't use primer and you have no seams to fill, then you can paint without sanding.

No sanding the parts isn't necessary at all,sanding is for after puttying or cleaning up seams.Enamel usually adheres well,if you are worried about adhesion,a shot of primer helps.

Hi & welcome

You should only sand where necessary, eg, seams, mismatched parts, joins etc., a little care on construction will pay dividends. a micro-dot scale plane is going to be small!

Avoid 220, leaves trenches that need to be filled, I use a file, or a scapel blade scraped across the seam, then 400, then 600.

I sand wet most of the time, smoother finish, less dust, rinse & allow to dry.

You shouldn't need to sand everything, unless the plastic is really rough, but it will even out the surface in preparation will help the finish.

Jon