well, you want the water to be sufficiently filtered, but if the filter creates so much circulation that theres a constant and fairly rapid flow of water, it will disturb many fish and can kill some. I found that by over-filtering my tank 50% with a waterfall-style filter, I created a pretty strong stream in the tank... which really stressed out my gouramis. If you can get a larger capacity filter with a less pronounced effect on water flow, that would work fine.

As for the heater... if you have the money, get one with a thermostat. I had a similar one to the one you're describing, and with the air temperature changes in my apartment, and such impresice adjustment, I had to check on it at least 4 times a day... which was a major PITA. My water temperature ended up fluctuating a LOT more than it should have.