listen pal theres a spray filler you can buy, not filler primer.
once youve got it all sanded back down using 600 wetndry then give it 3 or 4 coats of plastic primer leaving about 15 mins between each coat, the rub down with 600 wetndry gently, then use the spray filler lightley( should get it in one coat with right stuff) then sand down with 240 sand paper, theflat down with 600 wetndry, then paint in desired colour giving atleast 6 coats leaving 10mins between each coat, then leave to dry couple of hours and start adding lacquer coats atleast 10 coats leaving 10 mins between each coat then leave for a couple of days and flat down with 1400 wetndry and rub up with compound and polish.
but to be honest if youre not to confident about doing it dont as it will look a right abortion if done wrong.
good luck anyway pal