I have seen over 200,000 in the red before so don't sweat that. Instead of taking and holding enemy lands grab up 4 or 5 really good stacks and just go from provence to provence on a rampage. You will get some funds for pillage and if he abonds any provences distroy all buildings except the castle. Also note when his ships appear and in what seas. Rember it takes three years to build a ship so you know when to check back to blast them out of the watter.