i ll try to answer the first one .
base coats and primers are two different things
a primer like is for potecting against rust and also some primers will help to make a better bond between substrate and top coat.
candy colors are tinted clears so you need a base coat to reflect through that tinted clear. real chrome plating or polishing can serve as a base .
chrome like and silver powders are also base coats for candys .
if you want your candy to have a metalic look to it you can use a metalic silver as a base coat.
if you are just starting with candys maybe you should try with a red or a purple . much easier to get good results .