Regarding trade deficit or economic problems.

If you don't have enough money the solution is very simple but not intuitive. I think many players just miss that solution. You should have only as many soldiers as you can afford. Simple as that.

When playing Scotland for exampe the Nobles award me with some mailed knights for completing a mission. They cost me some 1000 florins per turn, there's no building I can build to neutralise that cost and at the moment I don't need them for anything else than parading around the settlement and my free-upkeep militia is good enough for parading and keeping the taxpayers quiet. The most logical thing to do is to disband the guys.

The lesson learned already in the STW is to have exactly that many soldiers that one needs, just as many to feel confident that you are able to repel any possible immediate threat or achieve the offensive goal and not one single mail knight more.