thanks will checkout
Ask yourself early in the project if the decision of choosing a an item - in your case, a customer - via a drop-down list is a wise one.
I can tell you that, for example, choosing a patient among 50k patients via a drop-down is NOT a wise one.
At a certain point you will be forced to give up the list and go for - let's say - a popover with a search field and a portal beneath.
Why not start doing it already ?
Thats a good idea