So I forgot to store up enough energy before i started attacking some planet. I kept attacking and even installed relays to overcome the energy deficit. My question is if I invade when the planet still has 10 population, will that mess up the chance of invasion success?... I can't afford for it to mess up. Its 432K when that is like 3 days income for me. It only has 10 defense and attack but I have no idea what determines invasion failure.

its attack score only on invasion. the more the better. so buy those big guns. invading at 10 will not affect the chance of success. dropping the planet to 10 only gives the chance to invade.