How can I use webform to upload assets and create a project that can be assigned to different users
if you want client submissions to become content I recommend EntityForm Then you could use for example the Workbench module to assure the content is moderated by a manager into approval.

You likely want your content type to show limited items to the client and then more options to the manager. I would try to do this with the Field Permissions module.

Lastly you could automate sending emails and stuff on some events if you want using Rules.