I'm trying the Rebel campaign and getting squashed in space. I can get past Kashyyk but then after a time the Empire shows up with a dozen Victories. I don't get how you are supposed to win against superior numbers and power.

Noob needs space advice.

Thanks.

So, everyone is playing this on medium for rebels?

The empire is way easier. At least I'm having fun. Vader sure helps with land battles.

The key is the use of bombers :). Bomber and fighter squadrons are fairly easy to afford and a large force can be maintained easily seeing as virtually every planet can strengthen it...
Could even throw in some marauders for anti-fighter support, and try saving up for a few strong units to base your formations around, namely Calamari cruisers.
3 x MC
2 x MC30
3 x Marauder
10 (?) x Y and X Wing
Depends on your unit cap of course. I sometimes forget mine is set to 60 for the Rebels.
Just try out logical combinations.