I thought about doing it to match the exterior. I can get spare interior parts for next to nothing, so I thought I'm thinking about giving it a shot. I know there are videos on yourtube and such, but I'm wondering how well the paint holds up over time, and what techniques to use to ensure there are no runs in the paint. Also, what do I do about the padded piece on top of the dash...can I even paint that at all?

 

Yes, hundreds, if not thousands have painted their interiors.
Here's some examples... cavalier interiors - Google Search

As far as paint types, just use a paint specific for plastic and vinyl.
It's all in the prep work. If you know how to paint, and take your time, it can turn out nice. As long as you don't go overboard.

Good luck with it.