Most people put the heater in the first chamber where the water comes in. The second chamber usually has chaeto algae and a light that goes on the back of the tank after peeling away the black paint. And the 3rd chamber most just upgrade the stock pump to a maxi jet 1200 or something.
I would do heater in the first; inTank media rack (filter floss on top, chemi-pure in the middle, and chaeto algae in the bottom) and light in the 2nd chamber, and maxi jet 1200 upgrade