Personally, I would be afraid of an infection or something breaking out and needing to deal with isolating / treating all the fish separately. Don't get me wrong, that sounds so awesome, but disease would be my main concern. With multiple tanks you wouldn't really have a problem on that large of a scale.
Okay so unfortunately my floor won't support 100 gallons. I read that one gallon weighs 8 pounds so that would be 800 pounds! What is the smallest tank size I could go if I only combined my community and my sorority?
Here are the specs again:
one male betta
one tiger Pleco
When determining what tank would be "too big" you have to take the betta into consideration. I don't think a big fancy rosetail would appreciate having to patrol around the tank with all that finnage. same with a dumbo betta. It would stress him out. He may not be fast enough during feeding time either. Plakats, females, and maybe even VT's however may be fine... I'm not really sure. Lets not be so quick to anthropomorphise our fish and say that bigger is always better. We have bred bettas in such a form that they become weak swimmers in comparison to other fish. In large tank you should make sure there are plenty of decorations and tall plants.
For the minimimum size tank for the combination of your sorority + community I would say 50 gallons.