I haven't looked at your code, but if you are using normal lua number (which seems to be the case, given the stated maximum) to store the amount of items, the limit of items you can store in practice is much lower, due to limited precision of lua numbers.

For example, for items with a stack size of 100, the real maximum is somewhere below 1e20, as the maximum number of items you can add in one step is 6000, and 1e20+6000 still equals 1e20 in lua, so once you reach around that many items, you wouldn't be able to add more.

In that case, in your example, the maximum would be reached in a bit more than three days.

Sorry, couldn't help myself from nitpicking - maybe you do something clever, in which case I' am happily looking forward to being wrong :)