Is there a limit on the number of items?

No, but lookups and lists, etc are obviously going to be slower the more you have. Though if you have high numbers of items, hopefully you're not doing much or any manual entry anyway. I've seen as high as 5.5 million.

We are a custom furniture business that does not currently have unique SKUs per configuration, contemplating changing that. Potentially in the range of 2M+.

The account I saw the 5.5 million in, basically everything back-end was maxed out (processors, queues, etc). I'd probably talk to your account manager to see if you might need to upgrade if you'd do this. There's nothing in the system that prevents you from having 2M items, but if that drags performance of the system down to where you need to spend a million bucks or two to get it back to "normal", that could be a pretty big decision point.

It should be noted- fun shit starts happening around 100k items

Appreciate that perspective