Though most ballasts have a warm end and a cooler end (so warm end up would be best) it is even more important to keep you lamp cords and mains cords separated as the lamp cords could generate high frequency feedback into the ballasts. And since all machines are amplifiers that is not a good ideaYou should of put all the same ballast together, and have them in all the same direction, just my OCD talking.
Mounting your ballasts vertically is always the best way, as it allows the air to move up through the cooling ribs. This provides the best cooling of the electronics, which is important, as heat is one of the main reason why electronics fail. Always keep them out of the light too.
Nice job!