In one game I am Playing I have about 25 to 30 planets (Abundant planets, huge galaxy). It is getting hard to prevent enemys from destroying my defenders, since I have alot of planets that are spaced out. My question is how can I manage a big empire and prevent the enemys from destroying my defenders.
Oh, and I;m only making 200 bc per month so I could barely afford mantaing 1 frigate fro each planet.
If you can't afford to put a decent defending ship on every planet, I'd examine your finances first. How much trading (trade routes) are you doing? Are you selling techs/ships to help finance things? What's your tax rate at? How much economic infrastructure do you have (banks/economic exchanges/stock exchanges/trade centers?).
I usually don't have a problem affording one of my best ships for each system.
Also, unless you're behind on tech, consider defensive ships, they tend to be less expensive to maintain.