If your line items carry the same names per category, export invoices with line items and build a pivot table: category as rows, sum of line totals and count of invoices as values. Average ticket per category is then one extra column.
I also build a nightly sync from Jobber into the owner's own Google Sheet that splits revenue by your custom fields, so sales, installs, rentals and service agreements sit side by side. Want a sample on test data with your four categories?
(Disclosure: this is my own small service.)
