dont need all the old paint off unless its a poor finish, ie cracks, reaction etc
just feather it back so its nice and smooth and each coat of old paint blends into the one underneath.
ide use P180 to start with on an orbital sander or by hand, fill what needs filling, rub down with P180 or maybe an old P80.
Finish with P180 then P320 to remove any deep scratches.
Can give it a wet flat with P800/P1000 or P1200 if you really want to, but theres no need as primer will cover P320 scratches.
Let your primer dry, depending on type.
2K (hardener 4/5:1 10% thinner) ide leave it overnight or at least a few hours.
Cellulose should be flatable in an hour or 2.
spray over the wheels a fine dust of black aerosol (matt/satin). This acts as a guidecoat, so when you wetflat the primer, any deep scratches will show and you'll be able to flat further and re-primer where necessary.
Wet flat primer with P800/P1000 or P1200.
Dry wheels and give them a good clean check the primer for imperfections.
mask out the tyres.
give the wheels a preclean with panel wipe then wipe with a tak rag if you have one.
give the wheels a few coats of paint. put it on dry and build the coats gradually til you got the full colour.
if you have lots of imperfections in the paint, give it a wetflat with some flatting paper, then apply a bit more paint.
let the wheels dry for 20 minutes or so under some heat.
give them another tak rag if you have one and apply a 3/4 wet coat of clear coat (laquer). This is a pretty wet coat of laquer but not enough to get a good finish, you do that with the second and possibly third coat.
the more laquer you put on, the more chance you have of it reacting/running etc. so let each coat dry for 10 minutes or so before applying another or it'll crack.
sit back, crack open a carlin and admire your handy work while it dries. any questions pm.