I never use any more than 1 pump with a sump.
The pump goes in the sump, pumps water back to the tank, and water flows by gravity back to the sump. I don't know where the idea comes from that 2 pumps are needed.
I have used commercial overflow, tried DIY overflows (with limited success), and now only drill tanks. Drilling is simple, and very inexpensive. Since I started drilling I have done at least 8 tanks, with the same diamond drill bit. Its almost as easy as drilling plywood, and takes no more than 5 minutes to drill a tank. I know glass drilling sounds daunting, but once you do it, you can't believe it took so long to start.