What seems to work fairly well for my (VH/M) campaign is to keep your military, except for the boats. Disband those as soon as you get your diplomat to the mainland. Sell anything you can via your diplomat and try to get at least half a stack of an army, but don't worry about going into debt, it will happen.

Luckily you can afford to have less troops due to Barae being a very capable general, and hit the two wandering armies that usually are the ones that seige your capital. After that, you should be pretty free to hit any of the garrisons since nobody will really leave their forts anymore.