If you always have the Audio files for a Project saved in that Project’s Folder then you can ignore Archive. It basically looks for audio you have stored elsewhere and copies it to your Project’s Folder in preperation for saving the Project by some other means (Backup, etc.).
In my opinion Backup Project… is poorly named as it implies it is part of some kind of backup scheme. What it is really doing is creating a brand new Project based on your current Project. This new Project will be in its own dedicated Folder which will include copies of all the Audio used in the source Project.
While this sounds pretty similar to just copying the Project Folder to a new location (which can work), there is one key difference. If you just copied the Project, when you open it it will look for its Audio in the Source Project’s Folder - which may or may not exist and you would want/need to to have the Project find the new location. But if you use Backup Project the new Project will already know where to look for the audio.
Save As… protects you against failure of the Project’s .cpr file
Backup Project protects the Project file and all it’s associated files.
For what it’s worth on a day to day basis I just rely on my PC’s system backups. So Time Machine may be all you really need. It’s really a risk tradeoff of what you feel comfortable with.