It doesn't matter if you get flat or glossy paint because once its on the tank and you are viewing it through the glass, it all looks glossy. The easiest way is to tape off the top, sides, front, bottom and trim with tape and paper then use spray paint. It's quicker and easier to get even coverage. Almost any paint with a roller will work fine also. Helps to wait until its completely dry between coats or the roller and new paint can lift the first layer if its still tacky. Obviously you don't want to get any paint on the inside of the tank. Make sure the tank is dust and water mark free before painting. If you paint over them they will be locked in between the glass and paint leaving an ugly mark.