Yep, thats the gist of it. If you have the time, money, equipment, and above all patients, a 300 gallon is better than a 150. Of course you will have to consider plumbing, sump, a floor that will hold a 300 gallon, and on, and on, and on. It will take a lot of time, research, and money, money, money.
As ageneral rule, the more water you have, the easier it is to take care of. Less chance for error.