C'mon now. You have to have some idea about a tank size. Okay....depending on your dedication to our hobby, maybe a 20g would be the next step up. I think bigger is always better, however. If you can afford the initial cost and have enough space, a 55 or larger would be my suggestion. Start with the tank size. After that, inspiration will come to you.
Okay, yeah I have room for a 55 and I also have the money. Just need some inspiration is all.
If you have room for the 55, you only need another 6" of depth to accommodate the 75. Go with the absolute biggest tank, you can fit in, and have the funds to equip. You'll skip the small to large tank train, that lots of people take!!