Glen,
the XS project currently gives you some necessary files such as .xsapp and .xsaccess, plus some default folders such as WebContent which are there as a template, but you do not necessarily need to have an XS project.
you may be able to create a general project if you want to create your own folder structure, etc, but make sure you do add the .xsapp and .xsaccess files in order to be able to run your xs code (xsjs or UI code.)
if you have a mix scenario where you have db code and also an xs app, you may either combine them into the same project or create 2 dedicated projects making sure you do group your development objects logically (js code, html, css, cds, sps, views etc)
good luck!