Umm did he say "sand blast" or tell you wall nut, bead blast, or soda or some other medium sand blasting isn't the best of choices for body panels it does produce heat and can warp some panels "not saying it will always" but you do run a risk
far as sanding between coat most definately the newer paints today are very touchy and require absolute smoothness, older laquers were alittle more forgiving but due to the EPA those are a thing of the past now if your going with a dark color make sure your body work is perfect dark colors will magnifie any inperfections
