you can build 4 volksgrenadiers without affecting your tech timings.
i've only ever made one post on this website, and it's wrong, so im gonna correct it.
4 volks is manpower draining in unfavorable matchups and will delay your tech. Even in fair matchups, if you misplay with 4 volks, you take bad fights, then you will delay your tech aswell. 3 volks -> tech -> MG34 is a much more effective option to deal with assault tommies while also being economical at the same time.