Re: spray painting over existing finish?
Yeah from what you describe it sounds like you should get the old finish off - everything will need to be perfectly level and smooth before you paint, otherwise it'll show through.
If you go down to wood, I'd also recommend a black primer coat, then flat black paint, then a clear glosscoat.. Flat black is so much easier to work with than gloss, and dries much faster. Then topcoat with clear when you've got it right. And my biggest tip, shake the rattle cans really well and make sure they're not too cold.