I have four tanks (one is betta-free though) - a 55g, a 20g, and two 10gs.When I was doing fish-in cycling on the 20G sorority and one of the 10G, it was kinda insane. I was changing water at least twice a week on every tank, more on those two. Now, I just do every tank once a week, and not massive quantites of water like I had to before.
Cycling will save your butt. If you want a lot of fish, divide up bigger tanks and cycle them. It cuts down on your work load. Or I think you can run several tanks off a shared sump system.
As an aside...I was changing so much water in heavy buckets for a while there that I actually pulled a tendon in my foot. Guess I can't handle 70lbs of water in bare feet! Believe me, constant water changes are no fun!
Beth, mom of two humans, and caretaker of eight cats and seven bettas. Yes, I'm crazy.