Ultimatly it depends on your strategy rather than the units you have, or don't have
I've gotten the hang of using the Rebels now, can destroy pretty much anything the demo throws at me with no losses. Using Chris' mod allows you to feel a little more about the game and how it will play. It's interesting, i think Imperials have strength of numbers, but i don't think they have many special abilities. While rebels each unit has a special ability. I'm going to enjoy flanking the rebel scum with my tie fighters and bombers and luring the rebels into a classic trap. I think the first thing you have to do as Imperials is be aggressive. You can't allow the rebels time and space. You need to box them in.
Or, you can use a unit as a tempter, bring their forces out, and flank them from behind with bombers to take out their prized ships. Bombers are surprisingly effective, espically against the larger ships.
Timing with this game is everything, and for Rebels it's knowing when to strike, the ships do move gently, they don't ever 'anchor'. So if a player ignores a unit for too long it will stray into open space and become a juicy target. I find this order to be the most effective: Shield Gen, Engines, Hanger, Weaponary. The more ships you disable, the more chance you have of winning. You could even let the ships live but keep them disabled. Giving the opposite player a fake lifeline.
Theres so much potential when it comes to the space battles. Can't wait to destroy you all with my cunning