You don't want the float switch,those are wired to a pump to turn them on and off to provide auto-top-off.The float-valve is mechanical,when the float drops,the valve is opened letting top-off water enter via gravity.I mis-read your post earlier,you have a Remora hang on skimmer.Your first baffle will need to go all the way up to just under the bottom of the 10gals frame.From there,it will overflow to your next set of 3 baffles.These should be approx 6",with the same over,under,over configuration that you illustrated in your first diagram.By haveing the 1 (approx 10")baffle isolating your hang on skimmer,it will perform the way it was designed to.By installing your next set of 3 baffles at 6",you will be able to keep the rest of the water level in your sump at 6" which should give you enough room to accomadate tank draining when pumps/power is shut off.AS for the T idea,you don't need to use that since you have a HOT skimmer.Just use your crash chamber adjacent to your skimmer and try to direct the water from the crash chamber close to the skimmer pump.You probably wont even need to do that as HOT skimmers have there pumps close to the water surface where the organics are concentrated at anyways.I would also advise to not go with alot of flow through your sump.400gph after head loss sounds about right.Any more than that,and your gonna have a very turbulent sump which will impede your skimmers peformance as well as cause a microbubble problem.