AH Supply uses clips to hold the bulbs in place, as do many T5HO lights. If you keep the bulbs spread out across the top of the tank, you might be able to run all 4 bulbs without getting too much light. The AHS reflectors do give quite a bit of spread of light, and I have no data for their T5HO kits, so that is largely a guess. I think ideally you would want 2 or 3 bulbs maximum running at once, with them widely spread out over the top.
It is much easier to maintain a tank that has only low to low medium lighting, and you can still grow virtually all of the aquatic plants that are available, if you use good CO2, which you should do anyway. But, if you really want high light, that can be fun, too.