First off you should have your skimer after your refugium. The way you have it now, the skimmer will take all the nutrients out of the water and starve the refugium. I would remove the second and third baffles and make that chamber larger and place the liverock and the refugium in that same chamber. I would then put the skimmer in the next chamber and the return pump in the very last chamber. Your heater can be put in with either the skimmer or return pump, wherever it fits.