That’s a more subtle issue, but yes, that’s a good general recommendation. In general terms, there are advantages to having your project reside in “neutral” territory, with the idea being that you can have multiple people having administrative access to the project without needing to be root. (e.g., when you have multiple sys-admins needing to deploy or troubleshoot the system) Another option having the same net effect is to create a specific account for each project and deploying the project to the /home directory of its account.
(I’ve spent virtually my entire career where the “principle of least privilege” has been an overriding concern.)
You shouldn’t need to. Pretty much everything in your configuration referencing project-relative directories should either be identified as relative to your BASE_DIR setting or relative to an imported app.
Your STATIC_URL corresponds to the location directive in your nginx configuration. The {% static %} tag defines a “prefix” to the url being generated as a reference. It’s that prefix that nginx is going to match to find which location directive to use to handle that request.