Since I'm still a ways out from the firewall forward, I opted to buy a power supply rather than powering from a battery. That seemed to work well since it powers at 13.8 volts and has up to 30 amps of continuous power. With just about everything turned on, I saw only a draw of 22 amps. That's probably the same amperage as one GE par 46 lamp used on my previous 172.
This was the first time anything had been powered up -- including the landing lights. Lots of items had been installed years ago, so it was nice to know that they worked out of the box.
Even so, there's a small punch list of items that I need to work through. I think many of them have to do with the control stick connections.