Seems OK for me.

Of course, I never played a game of AD&D where I reached 10th level. Good times

I think you're probably worrying too much about this. In particular, a Monty Haul one-shot is one where the PCs find a lot of treasure; if they start with it already, they're going to consider it as part of their character. Provided the adventure isn't baited with treasure, this really isn't much of an issue.