Hey,

first of all, i noticed not all units translated from empires to fog II as they are shown in Empire. I'm playing Colchis atm and all of the units i have acces to display quite correct but with mercenary forces things do change. There are different examples of medium infantry that just show as the standard medium infantry stack for that nation and not how they are portrayed. Do i need additional DLC for every unit to show up in their correct manner?

second military buildings. Once a province is named i assume every military building with a bonus contributes to the recruitment. So 2 baracks are unnecesary for example you only need one recruitment center of every unit? or does the 10% drill bonus stack?

no, you dont need the DLC, ageofd when create FOGE makes some mistake trying to "match" the units in FOG2 if you want the right unit for fog2 you have to edit a .csv file and replace some names, you can check in the slitherine forums for the parity mod, here is the link,
http://www.slitherine.com/forum/viewtopic.php?f=562&t=100420