You only need to prime it if you are painting a light color over a dark color. That is the main reason for it. If you are painting black modlings black then you don't really need it.

The adhesion promoter is available at any AutoZone or anywhere else you buy paint. You can probably get it at WalMart and Target too.

I can appreciate that you are a noob to painting but feel that you can paint. That is actually a good thing. Just remember what they said about thin coats. Don't expect this to be a 30 minute project. Give it all time to dry properly and use thin coats. Overspray the area you are painting so you aren't spraying it at one spot. So overshoot the thing you are painting basicly. Put them on cardboard or something so you aren't painting your garage floor.

If you aren't really aquainted with painting then you probably aren't too familiar with wetsanding either. That will help the project look more professional if you do that between coats. Do some research if you aren't too up to speed on it. Or get the paint from Lowes or somewhere that they can have someone there explain it to you and point you in the right direction. Its pretty important if you want it to look and feel professional.