I tried twice the game (the second attempt, I stopped at day 240) and for my third attempt I think I came to some solutions to my problems. The aim is to blitzkrieg, i.e hoard money and men until you have some decent reserves, and then in one sweep take 3-4 castles in a row from a weakened nation. Also I take care of not antagonizing any one but the weakened factions, so I will buy peace / be at peace with everyone but the crippled nation when I do that ....
I never exploit the game, so no one archer vs 300 garrison men or alternatively reduce battle size down to 2, etc. That would do a disservice to my fun...