im planning on doing that myself as well once i move off to college. i will be home 2 days a week, every sat-sun.
No offense, but I didn't know a single person who went home every weekend during college...even the people who lived 20 minutes away from campus. I thought I'd go home all the time, and I didn't. In fact my cat died while I was in college, and my parents didn't even tell me about it.Things might be different for you, but don't underestimate all the effects of college life.

Having 2 heaters won't matter. If the thermostat hangs so that it stays on all the time, one heater can still raise the temperature of the water to a point that it kills the fish.I will get 2 heaters for that reason.