I don't think you would necessarily benefit from VBA with this. I
think that this just requires some brute force.

Insert the three blank new columns  that you want. Insert three
additional columns to sum the 6+8+5 values. From here it is just a
sorting game. Sort the records by the column that adds the 6 other
columns. These are all a single category, right? In the one blank
column you can now identify these records as the common category. You
can add Validation to this column after you have classified them.

Handling those records with multiple purchases:
Adding a new column just count the number of transactions for any
single line. This would allow you to isolate the single purchase
records. Sort the worksheet and separate these out. That would leave
you with 1,000 to 2,000 records.

Again, this can be managed by sorting. Those records with totals in
more than one category just need to be copied and pasted at the bottom
of the sheet.

Does this help at all? These instructions are based on my
interpretation of what you shared. I might be missing something.