How big can I go while keeping the same light?

[TheReefGeek]

Also, understock where ever possible to avoid algae problems down the road.

Sure it is always possible to understock, but he primarily wants this tank for fish. I say load up, and stay on top of filtering the water. As long as the inhabitants are all peacefull too, they need a certain amount of swimming room, and an area to claim there own territory.

Lots of rock for bacteria, good skimmer, UV sterilizer maybe, and 15% weekly water changes. Monitor the nitrates and keep them reasonable, use RO water so you dont feed phosphates to the tank. This worked really well on my 50g with the above bioload.