Invoice naming

I have been using the app for about 4 years now. Cumbersome in a few areas but overall very functional.
I maintain a car collection of 125 cars. Customer wants an invoice for each car each time worked on during a period. I spend much time finding what I named an invoice to apply to current work. Need a way to capture the naming convention and increment.
Maybe could set a name for the invoice in the project data? Then apply increment for each invoice assigned. If blank can default to existing process?
Also need to be able to select several invoices to send out share. Or maybe just all unpaid. Sending one at a time is very slow.