It is possible to buy the bigger tank since the glass itself isn't the biggest expense after all. It's all the other stuff that adds up.
However, if your budget allows for you to purchase the tank, sand, salt, and flow, you could set it up simply at first and transfer the livestock. It would look pretty sparse at first, but the larger water volume will keep everything stable. Then as you have the funds, you can add more LR, more lighting, a nice sump, etc. What I'm suggesting is putting all the livestock at one end of the tank under a single light fixture. Ocean and Oreo could swim long distances into the shadows, so to speak, and come back home. Just like in nature. Sorta.
