lighting.

I would go 4 bulb.

 

+1 on 4 bulb. No sense in buying lights twice.

 

I don't think it's a question of IF you're going to get corals, I can guarantee you that you will want corals in the very near future. At first you will want any softies people offer you, then lps, then harder to keep lps, then finally sps. I think if you get a 2 bulb fixture you would have good lighting for everything except for sps. You could get sps with the 2 bulb, but(depending on species) you would just be keeping them alive, they would be much happier with the 4 bulb.

So in summary, I suggest the 4 bulb so you won't have to worry about what corals will do good in the tank, you will easily be able to keep any corals(light requirements wise). As long as everything else like flow, water quality, and stability are good you can have a very nice 40 long setup.

This is just my opinion, you could get away with a 2 bulb fixture as long as you keep a real good eye on your water parameters and keep up on everything in your tank, but having a 4 bulb T5 just makes everything else much much easier.

Good luck

 

Go with a nice 6 bulb t5 setup. When you get hook on corals, like most of us do, you will be glad you did.