1. “Ten years ago, Jon Arryn had given him a minor sinecure in customs…Within three years of his coming to court, he was master of coin.” So the earliest it could have been was in 292 AC.
2. No, the crown probably had taken on some debt, but Littlefinger magnified it.
3. Littlefinger absolutely committed accounting fraud (”trying to track some golden dragons through the labyrinth of Littlefinger’s ledgers. Petyr Baelish had not believed in letting gold sit about and grow dusty, that was for certain, but the more Tyrion tried to make sense of his accounts the more his head hurt. It was all very well to talk of breeding dragons instead of locking them up in the treasury, but some of these ventures smelled worse than week-old fish.”) but it’s also the case that the nobility of Westeros are not trained in finance.