I can not advise you on where to install new breakers. You need to ‘map’ out your circuits in your house. Which breaker supplies electricity to which receptacles, switches, lights, appliances, etc. National Electric Code (NEC) require that all breakers be identified and the list posted at the panel. Create a spreadsheet for your house, list each breaker, what receptacles are on that circuit, and the wattage of each item on that circuit. Total up your wattage to see if that circuit is overloaded. If you are uncertain about how to do this, then you need to call an experienced electrician.
My SENSE monitor shares the 30-AMP breaker with my electric dryer. As @MachoDrone stated, the SENSE unit only pulls a few watts. Because my electric dryer is not frequently used, if I need to turn off the SENSE unit for rebooting, then it’s not a problem for me. I have been using this setup for 4 years and never had a problem. Or you could use @MachoDrone’s idea.
Actually only the ‘black wire’ to the SENSE monitor powers the CPU. The black wire also monitors voltage on leg0. The red wire is only used for monitoring the voltage on the other leg1 (phase). If you have to reboot the SENSE monitor, then you only need to power down the black wire.
Whatever you do, take pictures. Make diagrams, take notes. You don’t want to be constantly pulling the breaker panel cover off to remember how it was installed.