The AI is bulking up close to 1,000 ships in neighboring stars.
Not to answer your other question, but 1,000 ships in an AI planet isn't very much.
First, realize that those 1,000 ships are likely to be spread out all over the planet. There will be a bunch around each wormhole, a bunch around the orbital command station/wormhole generator, and a bunch around each command post, of which there are probably going to be at least three or four.
In my experience, the hardest part about assaulting a planet is getting your scout in and alive. Sometimes it's not even possible. Then, you just pour your entire fleet through as fast as possible from the other side of the wormhole and establish a beachhead. You will probably take the largest losses at this point. Then, send in your engineers (or mobile repair ships; I prefer fleets of Engineer IIs and IIIs, although IIs have the effect (benefit?) of distracting enemies from attacking your fleet).
Once you have your engineers parked off in some innocuous corner and a scout somewhere hidden, you're now good to go. Your fleet of 400-800 ships (depending on level) should be able to walk through the planet as you'll only encounter 100-200 ships at a time. The AI might even be silly and send a steady, light stream of ships from each of his clusters, allowing your cruisers to pick them off as they approach individually.
Cheers!