While testing / troubleshooting, 12V is ok. Once you get it running, try putting it back to stock. The stock control has the safety controls to shut it down if there is an accident, etc.
Hook up the timing light as per it's instructions. Usually, there is a jumper and or a vacuum line to connect / disconnect - this varies by the exact engine and fuel system it has, best to check a service manual that covers what you have.
If you replaced the belts, it should be timed very close to where it was before they were replaced. I stopped bothering to worry about it, it's that close. As long as you didn't pull the distributor, and got the marks positioned correctly, it should just fire right back up.