My suggestion would be to buy a drive and create a back-up of the project and the media.
Only saving the project and the five minutes of footage you used for your edit will be of little use later if you want to make more than small changes. In this scenario, to make large changes you will need to batch capture the media from tape.
Here is an 80GB drive for less than $100.
https://www.amazon.com/LaCie-Desktop-External-300698U-Porsche/dp/B0000DC6AZ
This is not a specific drive recommendation; the link is provided to point out that there are inexpensive forms of insurance available.
Alternatively, back-up only your project file. If you captured with time code and your tape labels match the logged reel numbers, you will be able to batch capture all of your project’s media from tape in the future. This also presumes non-repeating time code on the tapes.
Only keeping the project file is the more conventional way to archive a project – the project file takes very little space. Using this method, It is imperative that you take great care in the logging process for your batch capture to work when you return to the project in the future.
There is no joy when things go awry.
That is why I recommend backing up your project and your media files on a separate drive. I archive this back-up when a project is likely to need to be opened in the future. It save a lot of time and head ache.
The Media Manager is the feature you should read up on in the manual. I use it for complex tasks that might be difficult to achieve without it.
In my experience, Media Manager does a good job with simple projects. However, speed changes, nests, and several other features tend to confuse the Media Manager.
Sometimes things do go awry.
Again, for this reason, I create comprehensive back-ups and keep them.
The cost of the drive space is worth the piece of mind for me and my business.
Here is a resource for researching the Media Manager.
https://www.kenstone.net/fcp_homepage/basic_onlining_jordan.html
And here is a source for the wheres and why-fors of the files that FCP creates.
https://www.lafcpug.org/tutorials/basic_files_stored.html
And here is a resource for thinking about archiving.
https://www.lafcpug.org/tutorials/basic_archiving_movie.html
Larry Jordan wrote all three articles.
Best of luck.
Tom