what size tank should i get?

I guess it really depends on what you'd like to do with the tank...

The 72 bow is a sweet size tank. I had the chance to snag one off CList with a sump an very nice skimmer for an excellent price, I just do not have the space so I passed.

I, myself, would try to sell it. You could do a sweet RapidLED build even if you let that fixture go for 1/2 the price. If you can do without a chiller, that's always a plus for energy consumption.