Hello,
I'm Msc in Computer Science and Engineering with 4+ years of experience in professional software development.
I would create the application in Delphi in which I have the most experience. It would have no external dependencies and would work on all windows versions.
I assume that it's a database that you want to store the data to. I suggest SQLite db engine because it's fast, easy to use and requires no configuration on user PC.
All the information you need (Customers, Projects, Products etc) can be stored in the database and searched/sorted/updated, and new entries added/deleted etc.
As for the Invoices and Receipts, what exactly do you mean by 'generate'. Should it print them somehow or save them as some file type?
Anyway I would have to know the exact details of your requirements to estimate the actual price and delivery date.
Let me know if you are interested, we'll talk everything through.
Regards,
Filip