I agree. The type of fish you intend should govern the type of filter. Active fish in long tanks will need more water current to replicate a stream, and this is part of the filter's job. Small fish from quiet waters in smaller tanks will not appreciate raging torrents, so less filtration usually works, something as simple as a single sponge filter hooked up to a small air pump.
As for heaters, don't try to go cheap. If you need a heater, this is the most important piece of equipment; a heater that fails overnight, either sticking on and cooking the fish, or staying off and freezing them, can wipe out a tank of fish in hours. I tend to go with the Eheim Jager heaters now.