RE: Nomadio React 2.4GHz Radio
I suspect that putting a regulator on your lipo will cause issues with the usb charging feature. You should probably be fairly deliberate about that as I suspect your lipo will be less than impressed with the react's inbuilt charger.
As for the regulator, several IC companies (I've looked at Linear and Maxim so far myself) make single chip 5v regulators that suit your power requirements for a couple of bucks.
Your circuit should look roughly like lipo - diode (to ensure current can only ever flow out of the battery) -> regulator -> react.
Since the react will now never charge your lipo, you might rewire the switch on the board in the foot to ensure that off really means off, and you'll no longer need to disconnect the battery when the unit is not in use.