Your task, should you choose to accept it, is to build a Customer Summary Report. It will need the following data (this should be columns that, when read across, form one row in this report):
Much of this data you can find elsewhere throughout the Zoho Suite but it is very useful to have it all aggregated up in one place. On the Customer record in Books, it would be a little difficult to quickly see the First or Last purchase. There is a widget to be able to see purchases in the last 12 months, but not lifetime totals. (Add a user filter to this report to be able to quickly search by name for the right account.)
In addition, beyond the insights you can find for just one customer, there are some very cool reports you can build using this data: