Unique Values and summing using Pivot table

Hi Experts…..need your excellent help again!

I have a single Master worksheet that will be added to at regular intervals.

The data is relating to invoices that my work generates, to which I need to grab information from this Master sheet (AllInvoices) and place that information into another existing sheet.

There are limitless numbers of customers and I need to generate a unique list of these customers and put them onto this other sheet (Unique).

I will then ‘grab’ certain relating information (such as total spend for that customer), and place that into an adjoining column of the Unique worksheet.

I think one option is to use a pivot table, but my boss doesn’t what to go along this line, and so I am getting a tad stuck!!!!

Could someone have a look at my attached Demo spreadsheet and suggest an alternative approach?

I’m thinking that the best approach would be to turn off the autocalcualtion for the unique spreadsheet (on workbook open) and then have a button which would re-calculate the values on selection, to stop the spreadsheet recalculating every time a new value / row etc is in-putted into the AllInvoices worksheet....but initially I need an approach to generate all the relevant values!!!

I hope that you can help, and if I have not explained anything too well, I have attached some hints to what I wish to achieve in the demo workbook.

Many thanks for looking at my Excel dilemma!!!