Thank you, Bryan! I'm trying to convince myself that all the extra work has been worthwhile, but am kind of saddened that my plumbing design created loud drains. Hopefully, putting in the capped Ts on the back of the bulkheads will substantially quiet the system. Also, putting on the hood & doors for the stand should dampen noise.
This project has definitely been a learning experience, and I'm very grateful to the BAR members for their generosity in sharing knowledge & skills with me.
I tested the auto top off system last night, with a MaxiJet 600 and some spare 1/2" tubing inside a 5-gallon bucket. The scary-looking contraption works! Will try to take a photo of the sensor inside the sump, connected to an extension cord. Basically, when the water level drops, the sensor powers the extension cord, which turns on the mini pump.
Contemplating ordering flow accelerators, now that I have cut back the flow from the main pump significantly. Good idea?
http://www.marinedepot.com/Pacific_Coast_Flow_Accelerator_Flexible_Ball_Socket_Tubing_Plumbing_Parts-Pacific_Coast_Imports-FT0033-FIFTFB-vi.html