I'll second Hungary being a difficult nation to play as while you learn the game. I've played the game for 71 hours now and understand pretty much all the mechanics yet when I tried Hungary I got pounded but for different reasons than you did. Right from the start I could never get my stability to 0 (which sounds like a low number but is actually the perfect balance you should always try to keep it at) because various events kept forcing it down to -2 and -3, I had a tiny army, tiny force limit (which is how many units you're allowed to keep in total, if you go over it they cost way more upkeep than normal), tiny manpower, tiny manpower increase when manpower was lost, no king, when I finally did get a king he sucked and so did his heir and the next one too (they sucked so bad I would have considered it divine intervention if I'd had just 1 ruler with 1/1/1 of each stat), I would never have won a war against any of my neighbours, not even the small ones but especially not Austria or Bohemia or Poland or any of those.
When I finally saw an opportunity to expand, Croatia (or is it Bosnia?) was getting beaten senseless by a rampaging peasant army, so when they had no army left and most of their provinces were besieged I fabricated a claim on one province, declared war, took it easily and made peace. Immediately afterwards, in less than 1-year, 3 rebel armies rose up in that province to defect back to Bosnia, which meant I had an army of around 30,000 men pillaging my lands and I couldn't do a single thing about them. My army was 8,000 men (6 infantry, 2 cavalry), my income was barely 1 ducat per month and I didn't have a hope in hell of hiring any mercenaries to fight the rebels.
So yeah, maybe Hungary is not the best nation for a first game, even though they look big and powerful =P
