Thank you very much for your reply.
Really very unpleasant. I'm under the impression that AL armies may walk around as long as they want and I have to accumulate funds for short-term military campaigns. Great wars are simply devastating for the budget.
How such imbalance is compensating? Only by human tactics superiority?
Yeah ... the CK AI is not very bright ... and even if he can have regiments mobilized forever without too much problems, you should still be able to beat him on tactics.
Big wars were very costly back then, and more than one nation bankrupted itself with costly wars. But in CK being in debt is not the end of the world if you have a good income.
There will be events where you have to sell of improvements, but there are also Calling Estates General, where you can squeeze extra cash out of your nobles.
If you want to keep in the black for large-scale wars, you need to think and plan.
using vassal tropps are free, so that is always a good plan ... and then just keep as much of your own regiments mobilized as you feel you can afford.
If you expect to fight a defensive war on own territory, and you have roads in your provinces, you can lower army upkeep to 0 without suffering attrition. As long as you stay under the Supply Limit of the provinces you are stationed in. Just remember to set it back up if you suddenly decide to go on the offensive

.... or your troops will dwindle away very quickly.