(I'll try to answer all points at once...)
Merc - good point, but I think that as moderator/GM, I could say - OK, you get half each / a draw, or a slight advantage to the defender. The main effect of that particular scenario would be to weaken BOTH the warring parties, exposing them to attack from a third party...
The other option (my preference) is that only the ATTACKER has to fight an M&B battle. Thus, only Wales' army has to fight in the invasion stage. However, if Denmark survives long enough to gather an army and counterattack (which they almost always would...) then the Danes become the attacker, and would fight an M&B battle.
Lots of battles! But does remove the win/win possibility
Yes, skill in m&B would be of assistance. However, everyone's characters will remain realistically close to each other, as the only levelling will happen in battles which are 'forced' by the RP.
Levelling your character by looting, attacking bandits, etc is NOT permitted. As difficulty must remain minimum 100%, levelling your character with in-battle soloing is risky. It is permitted. If it works, you become the hero-warrior-ruler, and well done. If it doesn't work (ie, you fall in battle) you will probably lose the battle, campaign, war, country...!
I have divided the map into areas with relatively similar power, eg the is only 'Ungarn' (and no 'Holy Roman Empire') which would not be too dissimilar to Bayern or Schlesien, two close neighbouring territories, in historical strength.
The relationship between M&B and the European territories...
I know, it's a bit questionable. And I am open to good arguments in favour of change.
I chose the Nords for England to give them powerful infantry as well as powerful cavalry, but not have the whole 'semi-russic' appearance of the Vaegir...
TDM - It might work better with a dedicated Europe mod, but I'd rather stick to native. The closest to a level playing field. Again, I'm open to good arguments in favour of change...
And, thanks for the interest. If you two want a kingdom/territory, say so and I'll reserve them for you.
First come, first serve.
And, I'm away for a few days now....