Well number one each model is different so you may get away with assembling the whole body on one kit and not another but I assemble as much as possible before painting. Primer and sanding will take that average gloss model and it will make. It super shiny. Makes a model just pop. Nothing comes for free it is a bit of work and time consuming but to get a great finish it needs to be done. If you know where to look you can get a full set of sandpaper/polishing pads and wax for $25-35 bucks (not positive on that its been awhile since I bought mine.) Again primers are cheap I prefer plastikote. And yes gray for most darker colors. Light colors I tend to go with silver primer so I don't get color bleed through