you would need to use a 600 grid paper/ from what im doing on my dash it seems to be coated with a layer of matt black so will need to remove that, then for prepping you'll need a spray primer, but you may need to get one for plastic OR that is actually flexible. good product is plasti prime -> about 30 bucks for a can, added with thinners, sprayed on with a spray gun! then rub that back with 600 wet/dry and then paint!! spray cans should work if you dont think you'll be needing to remove the panels again as it will crack when you put on/ take off! Can buy an flex additive to paint but wont be able to use pressure packs ( unless specially made in a colour matching place - see if they can add the flex stuff)
this may help, i'll be getting mine finished in next couple of weeks too!