Thanks for the compliment, and welcome to the boards here!
Your question is a good one! I also have a lot of trouble when painting joints. I believe that an acrylic matte finish is a good way to go... but it doesn't solve everything when it comes to the joints.
For ball socket joints where there is a part of the plastic that is going to be exposed and rubbed by other parts of the plastic, I have yet to find a way to keep the paint from coming off... I usually avoid painting these areas on a figure if I can.
For painting purposes, I prefer the old school joints used on most pre-2002 figures. I've found it very hard to paint around joints like the shoulder joints on the Preview Wookiee Warrior. If I do need to, I'll dry brush... a light layer of paint seems to help (at least for me).
Also, I have discovered the miracle of spray paint recently. If a figure is going to have a dark tone to it, maybe try spray painting it first with black spray paint (do not use the cheap stuff though). Spray from a distance, and do several layers of it each time after it dries. The joints seem to not chip. Then you can paint with your acrylics over it... I've only done this once so far (making a Darktrooper) so it may not work out on other figures.
Good luck, and I hope this helps some.