Hi!
I will be happy to help you with that. I have implemented a similar solution to what are you describing in a Google Apps Script web app. My app was used to send bulk emails and as a part of, we were allowing the users to upload multiple files as attachments. The files were uploaded to a Google Drive folder first, then sent as attachments.
For your project, the user will be able to upload multiple files, then the files will be saved in the folder created by the script. Then the folder link will be populated in the sheet in column N.
It will also create a new document for each client. I assume that you have a template document that you want the script to create a copy from it, then the script can populate certain fields like the client name in the document and add the date for example. Then the link to the document will be populated in the sheet in column P.
I will be more than happy to address any of your questions!
Sincerely,
Mohamed