The way I look at creating a missions is just preplan the operation you want to do. for instance a russian tank company has 3 platoons of 3 tanks plus 1 hq tank. How would an army use this force and against what?
You need to create 4 platoons and set to it same AI id.
For example if they enemies - EN1, for allies AL1 and than setup AI orders like viewed in manual (page 15)