Would a drop down box be able to update as new clients are added? and what would happen when the say the business expanded to 200+ clients? I feel that that would create more issues.
That is a valid concern. But consider this, on the quotes page, I'm assuming you're using a VLOOKUP to retrieve the data. That VLOOKUP is set to a specific table array (as an example, say A2:C6). So technically, the VLOOKUP as it is would not function if a new client would add.
If you're using the excel naming ranges thing, then it is relatively easy to fix up the VLOOKUP for new clients. E.g. you set the A2:C6 to be named DATABASE. Subsequently your formula will look something like: VLOOKUP(F2,DATABASE,2).
Now if you add a new client, you can redefine "DATABASE" to refer to A2:C7, which will now include the new row; leaving all the VLOOKUPs functioning correctly. Better yet, you could use a dynamic named range that will automatically update when a new row is added.
This is the same case with the drop box, it is set to a specific set of cells, but you can set it to refer to a dynamic named range. This removes your qualm about drop down boxes not being flexible.
I hope you have been using dynamic named ranges for your VLOOKUP formulas already. If not, time to fix that (or leave it for the testing table).