Heyho,
After finishing my Catholic campaign I started my Protestant campaign two days ago. Sadly, I have to say that it seems that this is the worst (balanced) game of Ageod I have played, yet.
Besides the missing prisoner feature, which is a really weird thing, because obviously parts of it are in the game, it is impossible to keep a large army as the Protestants. After I got more troops through events, like Denmark joining the war, my maintenance costs rose to 7 gold per turn.
Even with several regions under my rule, I lose as much money as I get, meaning that I cannot recruit new units or even replacements. Funny thing is, I keep losing lots of units due to historical attrition, but the costs stay at a high 7 golds per turn. There is no way out of this dilemma.