Jim you have surmised correctly that the airplane will only be in balance at the point you select if it sits level. The 'support beam' is the main spar. Most airplanes especially trainers will have the spar at the quarter chord (aka 25% mac, mean aerodynamic chord) and this is the ideal position to balance your airplane.

The lead is OK but as others have said sometimes other shifting of components is helpfull. Such as if you do not already have the battery all the way forward behind the firewall and under the fuel tank then I would suggest doing so rather than the lead.

Enjoy your maiden.

John