Hi, I'm an experienced javascript/angular developer, new here at freelancer. I have worked in several google spreadsheet addon.
For you requirement, it's the best choice to go with google sheets and scripts, since it allow you to easily extend or add any additional features.
I can create you a google script which generate the slips and sent to to the users. Do you want to use gmail or any other email service provider to send slips. It would be great to discuss in detail in a chat, drop me a message to discuss further. Looking forward to hear back from you.
Cheers,
Padhu