BoG Goku has 100 years of prep
BoG Goku can't die of old age
BoG Goku has full knowledge of how powerful galactus is.
BoG Goku can use the time chamber, no limit for the time chamber he can use it as much as he wants.
BoG Goku can use any training equipment he wants in the 100 years.
BoG goku can breathe in space.
Galactus is fully fed and has UN.
Win by death.
Place to battle:
If whis stated that bills can destroy the solar system in an instant ( it's probably true since whis trained him and he has no reason to lie ) , and those guys has the reaction of MFTL ( Seeing how vegeta base form at 400x gravity dodged multiple lightspeed attacks ) , instant for them should be AT LEAST 0.001 Seconds, therefore bills can destroy 1000 solar systems in a second.