I would go with the MJ 900, I do not believe you will be able to provide too much water flow. If the velocity is too high, you can diffuse it with very little loss in flow. As for the heater, I would use a 150W heater on a 29g, or better yet 2 X 75W. As a rule, if there is a possibility of a cold winter (like up there in the north) I recommend 5W per gallon, in warmer climates (like here in sunny FL 8) ) I recommend approx 3W per gallon. 2 undersized heaters builds in a fudge factor, you know Murphy and his laws....If one get's stuck in the on position, it is not powerful enough to boil the tank, if one fails, the other will still run to provide some heat....