RCS do not need a heater. Unless your house temps are literally freezing. Once the temps drop below 65 breeding pretty much stops, but otherwise, they actually do better at lower temps IME. I keep mine, and other similar shrimp, from 68-75.
A filter is not absolutely necessary, but since shrimp are sensitive to toxins like ammo and nitrite, and like well oxygenated water, it is a good idea.
I would recommend 1 gal
minimum for RCS.