I have it sorted out now.
I was mainly looking for a way to redirect my site from the base domain name to a subdomain, without losing my content on the base domain. If I'd used domain forwarding (through my hosting company) it would've uninstalled things, but I redirected it using the .htaccess. I also changed another of my sites by changing the domain forwarding there to regular hosting, and adding a .htaccess file there too.
I found I could still access my files stored in other directories on the base domain, but if a file was missing (came up with a 404 error) it redirected to the new site, but I figure that's alright/not that big a deal.
I also picked up another domain for a free book promotion site a couple of nights ago and I'm going to build that one, but I've been doing research on themes and the best way to go about it (without having to spend too much).
I was also having this problem where when I entered the www domain on my computer, it always came up with /nonexistent/ and said it couldn't find it. But if I hit enter a second time, it would sometimes work. It only seemed to be on my computer across all my browsers, whereas it loaded fine on other machines and on my phone. The changes I made seemed to get it working fine in my browsers again (I also whitelisted my sites in case that was interfering).