AaronT: thanks for the advice. I've now had multiple folks recommend going with the larger canister so I'll certainly be on the lookout for deals on the xp3.
As far as the lighting goes... like I said above the original idea is morphing a bit.
Thinking of using a 2x54w T5HO in addition to the 48W and doing pressurized co2 now.
I'm not in a huge hurry to get running so I want to take my time and do everything nice and neat the first time. I'm concentrating on figuring out the plumbing first.
Even using the port as a return I still have the same question regarding the bulkhead fitting in the hole and maintaining a seal. I know the bulkhead is only a $7 part but if I'm going to do this I'd like to order everything at once to save a bit on the shipping.