If only people that attend a Course should have access to files, then you will want to restrict the files to registrants when you upload the files.
Registrants could access the files by searching for the Course even if they were marked complete. If they were marked complete, they could not view the files by clicking on their registration. If left as registered, they could view the files by clicking on their registration.
If anyone can access the files, then do not add a registrant restriction. People do not need to register to view the files and can simply search for the Course to view the files.
We do not have a restriction on the number of documents that can be attached to a Course at this time.