There should probably be a minimum amount of items they can actually incubate so he can't have 300 coins at once.

Magical items don't happen often, probably would be like blessing items, in which case they'd have to be fairly weak for any chance of copying (and presumably the blessing holder can turn on/off the blessing as needed) AND I AM ASSUMING YOU'RE NOT GONNA LIKE PULL OUT 300 MAGICAL ITEMS OUT OF THEM, secretly stockpiling FOREVER, so we should be ok with that.