if the body's straight and you need no bodywork, just wetsand the whole car and use a sealer before you shoot your paint. if you do need to do some bodywork, just spot prime the those areas, I'd stay away from Lacquer primers and use a good 2K primer, no need to prime the whole car if thats what your saying. but it's always smart to use shoot a sealer over the whole car before you paint, i believe you can get a white sealer too, after you shoot your sealer, you can shoot your paint right after