Generate random combination of letters and numbers fith fixed length

This is all really interesting. One of the hindering details is human readability/utility.

For example, if a user needs to search customers by ID. In this situation, more variables (letters, caps, length, etc.) that increase unique probability, would at the same time make data entry more difficult.

I am wondering if sequential numbers should be a function in menu dropdowns?

For the discussion of unique IDs, it would be nice, but not required. However, anything dealing with finance or accounting, this is necessary. Some countries require it for tax purposes, and eventually, ill need to do it for invoices. Super important to have sequential invoice numbers for order tracking in our industry.