A. "the number of ships on non-neutral planets increases according to the growth rate for that planet."
What does "according" mean - simple addition? And what happens to the neutral planets - no growth? In which case, how many fleets do the neutral planets start with?
b. "If the result is less than zero, then your bot gains control of the planet."
And how many losses have you incurred - exactly the number of defenders? If the defenders win, do they suffer losses equal to the number of attackers?
The reason I'm asking is that, if all the game does is simple addition and subtraction (no defense advantage, no Lanchester-type law for combat), then there probably exists a very simple optimal strategy, and it's more a problem of mathematics than AI.