wheelliftnpony

ok i just bought a 4cyc that me n my brother n dad are turning into a 5.0 its a 88 hatchback lx.. someone painted it with a house painter.. to paint like siding on a house.. I want to sand everything and prime it..then im taking it to a professional to have it painted. I dont wont a million doller look.. but i do wont somthing decent. ok im starting on the sanding part. What sand paper should i use and how far down should i sand? im taking off the doors and hatch and hood to do every lil spot. the car is red right now, even know its kinda orange peald lookn cuz of the guy that painted it with the house sprayer... but im thinking of going all yellow with 3 stripes going around the sides.. the bottom of the sides.. black red and grey... or i might go a real nice metalic blue.. im not quite sure i didnt know if it matter how good it is primed and prepd for the lighter color's or not... thanks guys