I used to have luck with bolstering squads before teching up, considering I saw ostruppen before the choice was given to me. Then teching up and unlocking weapons and giving each squad 1 bren (give them 2 adn they will always drop one at vet 3 :/).
Recently though, I have had no luck with that at all and I just can't keep up with the sheer number of them, what I have learned though is:
1) Take and hold key buildings as well as you can, getting them out can be an absolute pain.
2) Get at least 2 vickers and place them on your flanks.
3) Use a sniper to fire on any gren/engie with flames/MG's the enemy will bring.
Going Bofors might be a much better choice than going AEC due to the fact the OST cant do anything against them but they can faust the AEC. A mortar pit in a defensive position would possibly help too but these two are speculation as I have yet to try them but I will certainly do so when I next see the dreaded prostruppen.
AEC is definitely good against Ost when well micro'd because if you avoid their AT guns and harass Grens from a distance they can't do anything but Ostruppen can lock you out of the game right away due to the fact that they can win a war of attrition.
Although I guess it's map dependent, the CoH1 maps are unbalanced in CoH2 due to having insanely important buildings. Can decide the game really early on if you can hold one of them.