G'day Hagar
Welcome to planetFigure, and welcome back to figue modelling.
To get you started, may I suggest the following basic colours for your oil paint collection, and then a few more to get once you're going.
Firstly, I'd start with white and black. I suggest Titanium White (because the titanium gives the best coverage) and Lamp Black.
For the colour palette, start with primary colours red, yellow and blue.
I'd go for a Crimson rather than a scarlet colour for the Red.
I use a straight Yellow colour for yellow, and Prussian Blue for a deep dark blue.
Theoretically with these five tubes of paint you should now be able to reproduce every colour in the rainbow by blending these 3 primary colours together and varying the contrasts through application of black or white. As we all know this doesn't stop determined figure modellers from buying more tubes of oil paint.
I'd recommend you add to your basic collection by purchasing Olive Green, Burnt Umber (dark brown), Naples Yellow (light sand) and a flesh tint (if you can find one).
I'd also recommend you get yourself a colour wheel and stick it in front of your workbench. This will help you learn how to choose the right mix of colours to create various secondary and tertiary colors.
The best advice I can give you is to select a really good quality sable brush. The best paint in the world will still look bad if applied with a cheap and nasty brush.
The use of mediums is a matter of personal choice. I know some people who swear by them, and others who've never used them. The results are no different.
You may want to buy some Testors Lusterless Clear Lacquer, which like Dullcoat, helps remove the natural sheen oils produce once dry.
Hope this helps get you going Hagar.
Cheers