For your filter question, the cheapest solution is to get a sponge filter. I use multiple sponge filters in my smaller fish tanks. They are powered by my air pumps. I can adjust the airflow directly through my Rena Air Pump and an air valve on the air tube, which in return controls the water flow pulled through the sponge filter.
I use Hydro Sponge filters myself, a Hydro Sponge I is good enough for a 10 gallon, but the one new product Oxygen Plus looks better with the air tube in a separated entrance.
Another option is to get an AquaClear power filter. I am positive it is adjustable, although I am not sure exactly how low of water flow can it reach. I would always put a piece of small sponge pre-filter on the intake of such filters to avoid something being sucked in, which in return it actually reduce the water flow very slightly but increased biological filtration.
