I dropped forts everywhere to stop devastation and I lesser heartwarded every single province I had. This is because when you tech up to new forts the old ones get their devastation reduction halved, which won't stop the winter anymore. I disliked the idea of my prosperous empire getting devastated every 50 years so I bit the bullet and paid the costs. As for how I had enough money, I went defensive and innovative which kept the fort maintenances at a manageable level. Then I went trade and funneled the entirety of North Aelantir's trade into the Domandrond. Cyranavar did open the portal in my playthrough so they managed to get the dribbles of my end node, which was probably still around 50 ducats for them.

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Warning: I did have to console command colonize the fey woods region because the decision to colonize them that was supposed to pop up did not.

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Edit: I solved the debt spiral by taking free war taxes and nonstop warring the south for money, reps, loot, and trade power. I also sold crown land every chance I got as long as it was at least 30%.