Is there a way that I could have users create accounts with a p5.js program, which would be used to load stored data? I would need to know how to save data (specifically arrays) to a system such as local storage, and then load that data based on which account is in use.
Answers
You can certainly use local storage to store data on a user's machine; but what you describe isn't going to be possible; unless all the users are accessing via the same browser on the same PC...
Any kind of secure, authenticated user account normally requires some form of server side code.
Any suggestions of server services available to do this? I can picture doing this using PHP for managing files on the server side. Could p5.js be used while running on the server side?
Kf
Use whatever server-side technology you're comfortable with and have easy access to ;)
In principle p5 should work with anything that has a REST interface...