Again, it sounds like they are trying to over-engineer this and potentially opening up all sorts of other considerations.
It depends on what they want:
Option 1: Each item is the same, off the shelf. In which case, all they need is a digital download shop.
Option 2: - Like freelancer - they want individual client accounts/project management capabilities like updates/revisions/downloads etc. ( you won’t find it out of the box. )
There are client management plugins but integrating these with a theme/template and making it all work together is not a basic job and going to require some significant development skills.
On top of that, to include that type of functionality requires other considerations like robust hosting and security (that’s a lot of confidential data to look after) and the costs involved, most likely a fair amount of maintenance.
I think your friend needs to give you a proper site map and UX