So I was right, you want faust whenever you build T1 or not. You want Ostruppen spam + faust with your BP1...
(Damm my plan to have Osttruppen secretly buffed and conquer the world was discovered...)
On a serious side now. The post is mostly for grenadier and grenadier's faust is separate issue from Ostt.'s faust.
If you want to know my opinion for Ostt. here it is:
"Ostt. reserves" should have faust even if the T1 is not built
Ostt. from "relief infatry" should have faust even if the T1 is not built
Ostt. call in should have access to faust even without a T1 built if it is delayed enough, if the overpeform in anyway their performance should be looked at and not their faust ability.