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You want to install the pump on the return at the bottom of the tank not at the top of the tank. All you need is a 1/2" return line. That's why Grundfos only makes a 1/2" pump. You also want to remove the tank drain, install a 3/4" brass nipple then screw on a 3/4" X 1/2" brass TEE. Your drain goes into the end of the TEE your return into the 1/2" branch. If your pump has a built in check you don't need another one. An expansion tank is only necessary if you have problems with the temp & pressure relief valve discharging. You can install the expansion tank (if you need one) on the cold water line near the tank.
The return pump always goes on the return line at the bottom of the tank in a case like yours. You're only moving enough water to keep the water in the line hot. Why do you suppose Grundfos only makes a 1/2" return pump when every water heater has 3/4" inlet and outlet connections. Your plan can work except that you're significantly reducing the hot water flow to the fixtures by reducing to 1/2" to accommodate your pump. Stick with the config that's standard practice.