The battery does not power anything when the motor is running. you are running off the alternator. The battery is a reference voltage for the voltage regulator, and a storage area to supply power to start. Once you are running, it also smooths out the voltage from the alternator a little.
A 750 Honda uses a 14 amp hour battery, my CB 360 uses a 12 amp/hr battery. However, you need to consider cold cranking amps. Between 150 to 200 CCA will give reliable starts. You can start on less, but the Honda ignition system doesn't like low voltage, and if the bike doesen't start immediately, the voltage may drop low enough on start that you will not have a spark.
Also, running less load means the alternator will generate more than you need. The battery will stay charged, but the voltage regulator will be dumping more current then usual. Hopefully you have a newer, higher capacity regulator. The regulator works by creating a load high enough to keep the alternator output voltage in the right range. If you removed all lights, the regulator may even overheat making enough load to keep the voltage within specs.
