The Morningstar MPPT is one of the best and a good choice and yes if you feed the load through it there is a limit. However I wired our Sun Saver MPPT so that it feeds only to the 150AH battery.
You may be a bit light on the wire you may want to check the voltage drop http://www.calculator.net/voltage-drop-calculator.html
I used 10ga because I have a high voltage panel and the voltage drop is not a concern, and the controller sits on top of the AGM battery and the wire from the controller to the Victron battery monitor shunt is in inches.
