Just call down Turret Control first thing, get an A-V and A-I, at the same time, get a full load of stormtroopers right away to man the turrets. The first two or three hectic battles, you'll have enough CPs to bring down about 6 Mobile Artillery. The MAs will whomp any troops and leave a big dent in the invading vehicles. Be sure to bring down a Repair Droid (can you do this?) to fix up the turrets and MAs.