You could buy some UV Sensitive Paint. I believe Xoxide sells small canisters especially for modders that comes in different colors. Turn that bland bare metal into something a bit more aesthetically appealing?
The bare minimum of a water cooling loop includes:
Pump
Radiator
Water Block(s)
Tubing & Clamps
Coolant
I believe that's all you would need to run a water cooling loop.
You can get clear tubing for water cooling loops and fill them with UV reactive coolant. It's a pretty popular thing to do among PC water cooling enthusiasts and the like.
The best way to replace a shiny paint job with a matte paint job is to rough it up with sandpaper first and then paint it. Make sure that you hold the aerosol canister at a distance so as not to cause paint dripping or an uneven spray, where it's thicker in some areas and thinner in other areas. Well, that's not the *best* way, just a basic way with some decent tips.
I'm no expert with matte paint, so maybe someone can give better advice.
Just make sure you don't cheap out on aerosol canisters. Cheap canisters like to sputter and/or don't give very even/fine sprays. I forget what brands are the best, I'm sure someone can suggest some trusted brands though.
Hope that helps!