A couple of notes :-
a) you can only add dormant divisions this way - so you do need to specify them all in the INC file first.
b) Just using the "strength = 80" line only limits the starting strength - if you wish to represent a smaller than Division sized unit for the longer term, you can try to use the "max_strength = xx" line as well. I say try because the problem is that your understrength unit still has all the attack and defence stats of a full sized unit - hence your "Brigade" will attack just as well as a Division... all it will do is die rather sooner because it is only at (say) 30% strength.
Typically, a German Division would be 15,000 men strong or so - a Brigade or Regiment would be about 4000 men, as there are 3 Brigades/Regts in a division, plus supporting troops like artillery, recon & engineers. So 1 Brigade might be about 25-30% - but see my caveat above about trying to model this.
Tim