Number 1) Shouldnt be - one of the most important things! - Cons - dont lose any unit! Try it!
2) It depends on the situation: Map? Many houses? Against which faction? I play with 3 Strafbats and they beat the shit out of the enemy. Against OKW Maxim spam does well (3-4 Maxims)
3) 13 Min: No!
Key 2 win against OKW in my eyes is destroying their HQ's: You make this with 2 katjushas shooting at once time. ;-) I win nearly everytime with it (in 2v2/3v3/4v4)