You only need one gate valve if you use it to control the 'MFL'.
This is how my 120 is set up.
I have a 4 way [ + ] that goes from pump to my two returns and then to my open line that flows within the sump. It could just go anywhere ? I have the gate valve on the "open line' to control return to tank speed.My open line goes to a UV
but possibilities are wide open.. Think 'manifold' if you wanted DIY caniters in the sump and pump is powerful enough...
Make the last section where pump is as big as possible so you don't need to top off every other day...IMO
baffles /overflows are highly overrated ,and to be used as a tool to direct water flow for use in the sump.
I also use a digitally controlled DC
pump to help with flow control.