First off, 45 stars can be obtained without getting 3 stars on each mission. I unlocked this at campaign level 19 with 3 stars on the easiest ones and 1 star on the harder ones.
Troops:
I would go in with cheap troops Rifleman (Barracks), Fighter (Hanger), and Gunboat (Shipyard). These take the least time to produce so you don't have to wait longer than 10 minutes to refill. Dump all your troops at a single point hope you come out with more stars than you started with. It can also help to add a few Motarmen behind the Rifleman and Ranger (if you have it) with the Rifleman.
Leave 1 troop (any type) in your inventory so if you don't make the progress you need, go to dash and quit game. When you load the game back up, all your troops will be back.