This was only the start  of this project and I will be developing it further.
Your suggestions will all be part of the solution, I suspect.

My ultimate goal is to be able to have:

- Several separate sequences intermingled
- sub-sequences
- the ability to use Arabic (ordinary) numbers, roman UC, roman LC, alpha UC,
alpha LC
- to restart sequences
- to run sequences across many sheets or a whole workbook.

I have in my mind how to do this but I needed a firm foundation for this.