Hello, I've gone through the script provided in the link given by you.
The script looks complete and would only require testing to check if it works properly, In the script the file is sent as an e-mail attachment if size is less than 20 MB, but you've included in the project bid that you want to share the download link. I don't think sharing downloading link is a good idea as that link can be then shared to other people and they can download the item without paying. I suggest using url shortner which will change the url and procvide and url which exists only for a particular period of time.
I'll be able to deliver the project within 2 days.