My idea's for the multiplayer are:
Muskovite:
Inf's and musketeers are good enough.
The cav needs to be improved with better bows and muskets.
Polish:
Inf's and musketeers are good.
For the cav the lances need to have less damage or cost more.
The bows need to take longer to draw so you can shoot about 2 times in the time that a musket reloads and worse aim when riding but for standing still I think it is ok.
Sweden:
The infs are good.
The musketeers need to have worse aim or longer reload time.
The cav armor and the aim for the muskets is good I think but the muskets need to do less damage.
Cossacks
I think the infs are good without good armor because of their speed you can dodge bullets better but the spears are to fast so you can very easily spam someone (I am guilty of this).
The musketeers are pretty ballanced I think but maybe a little less damage.
For the cav I think worse aim (like the swedish cav is now) or less damage so you cant one shot people.
Crimean
For the infs they have to get worse aim for the bows and better aim for the muskets (I dont think they need more weapons because of the bows that they have).
I dont know much about the lancers (I never use them) so I have nothing to say about that.
Ofcourse the bow cav needs to have less accuracy and also less damage plus longer time to draw the bow.
For the maps the glitches need to get fixed the rest is not as important I think.
Also having two more smaller maps (like market place) would be great.