You can do a lot in a pico. Just keep up with water changes. I highly recommend you do not put sand in the tank. A heater is not needed unless you keep your house especially cold. Depending on what pump(s) you use they will provide enough heat.
Here is my 2 gallon (8x6x8) it's been running over 4 and a half years. I use a par 30 for lighting.
