Welcome to JD, I think you'll find this site is full of customizers ready, willing, and able to help out.
Now to your question. I've never done this but I've heard others talk about using enamel based paints (such as many Testors paints) that always make the figures sticky. From what I understand, the paint actually reacts with the plastic in such a way that it never really dries. I'm wondering if that is the stickiness that you are seeing.
If you are painting on plastic figure, best off using acrylic (water based) paints. You can buy these cheaply at a craft store (e.g. Apple Barrel brand and others, including testors acrylics) or more expensively (Citadel/Warhammer, Reaper, or Vallejo are all brands commonly used by forum members). For the most part, I've seen that "you get what you pay for" when it comes to paints. However, almost any acrylic paints should work.
However, your main question was on Matte coating. I've used these sprays off and on on my customs. I'm on the fence as to how well they actually work. I've found that sometimes the sealant actually leaves the figure sticky but it usually dries given enough time. I know a lot of other people here seal all of their figures and that usually helps with minor paint abbrasion.
Good luck and make sure you come back with photos when you are ready!!