Not much to be added, after good explanation by Ernest.
I always, almost exclusively use acrylics for the base coat, as it gives strong base to work with. Do not forget to use the primer first tho!
I sometimes use enamels over the acrylics, but i first make sure the acrylic coat is 100 % dry.
Its good to experiment on the bit of scrap plastic first, as different brands sometimes interact with each other, and its hard to predict the reaction. Usually it looks more scary than it actually is.
I have never had problems with oils, or MIG filters (by saying MIG filters i mean SIM Industries filters, which are marked as MIG product).
You have to be carefull with the varnish tho, as some of the brands are difficoult to work with under certain humidity conditions, and can turn milky.
Im using Tamiya acrylic varnish, and Hannants one with good effect.
Good luck.