On our playthrough, we have encountered a number of problems using this mod.
FIrstly factions like Tilea, Tobaro, Lyonnesse, unit spam like crazy. There is no feasible way they can upkeep those units at all. Lyonnesse is making 500 a turn through its only settlement plus 2500 base income, it has 3 armies, 1 full stack and the others around 12 - 14 stack. There is no way ever that they are sustaining those armies. Tilea are doing the same too. With the Garrison upgrade as well, there will be 2 armies standing on a 20 stack garrison when you encounter any of the weak 1 settlement factions and its terrible.
They shouldn't be that strong and shouldn't be unit spamming or be able to sustain that level of army capacity. I know there is difficulty but that is over the top bad.