You can add a fan at the top. The fan you would want to be exhaust as hot air rises. So far Ive got two custom built cases going on. For my case mod stuff I go to thebestcasescenario.com. There are some awesome cases being built over there.
As for painting the inside. Most any paint you will be fine with. What you are going to want to do for a really nice paint job is to dissassemble the case. Any thing that can come out your going to want to take it out. For some cases your going to want to derivet the drive bays and such. ANd rerivet once everything is down. If you don't then your going to have a hard time avoiding running paint and such. Its easier in the long run to get a nice paint job by taking the case apart as much as you can.
Then sand down everything lightly with like 220grit sandpaper. You just want it to be lightly sanded so the paint sticks well to the surface. You don't need to use a primer if you don't go all the way down to the bare metal. If you do, then hit it with a coat or two of primer.
Once you've sanded everything, then hit it with a few coats of paint, sanding lightly between each coat. Then to protect the paint, I would hit it with a few coats of clear coat, again sanding lightly between coats.
If you want a real nice gloss finish, then you progressively lightly sand with increasing grit sandpapers. 1000, 1500, 2000. You want to make sure you put quite a few coats of clear as you don't want to go all the way through the clear with your sanding. Then use some rubbing compound and get to it. After a while of rubbing you should have something extremely smooth and shiny, like a professional paint job.
If you just want to paint it and don't care about how it looks really. Then just lightly sand it down with 220 grit or so, and spray it with a few coats of paint, let it dry and call it a day. The above takes a lot of work, but will leave you with a beautiful finish. Something you can be proud of.
Hope that helps.
