how would that work out with my existing CentOS cPanel server running Litespeed instead of Apache as a webserver, with a dozen other websites on the server already?
What tweaks might I have to perform to make this Discourse install work properly on just one of those sites that requires it?
You can’t follow those steps. You’ll have to configure it manually and make light speed reverse proxy. See How to set up Discourse on a server with existing Apache sites as an example. If that server has less than 4gb of ram, I’d recommend that you spin up another so that you can do it the easy way.
Yes, you can do a subfolder, but it’s really not recommended. It adds lots of complexity and mostly no one believes that using a subfolder has SEO advantages, best I can tell. That said, I think that some hosted client(s) has subfolder, so it should work.