I'm a little confused...
Ben's FAQ said to create a domain on Plesk with username.freepgs.com. Easy enough. If I have a domain name, I change the nameservers to point to Plesk, then submit a help ticket to get it added onto my site. So in this case, Mydomain.com would point to username.freepgs.com, yes?
So if I have other sites I wish to add as separate domains, are they set up as subdomains off this main site? Or do I create a separate domain in Plesk for each one?
I'm not sure I understand exactly what you're asking, but I'll try:
If you have a domain, there's no need to fiddle with any of the username.freepgs.com stuff, just point your nameservers at plsk1.lvcs.net and plsk2.lvcs.net.
All the domains should be added through Plesk.
So I don't need the username.freepgs.com at all. And if I have, say, three domain names, I enter each of them via the Plesk control panel (not as subdomains). Then point the nameservers for all three domains.
That is correct.