So my site can't handle on a shared host anymore and I'm moving to a dedicated. I'm planning to have cpanel running just my site for now. So I already own, let say, domain.com. Now that I have a server, I heard that you shouldn't set your server's fully qualified domain name same as your website's domain (domain.com). So does this mean if my server FQDN is like abc.domain2.com, I have to buy another domain name called domain2.com? I just want to make sure that this server will email correctly without email being blocked. I know how to setup RDNS, but yea. Thanks!

So does this mean if my server FQDN is like abc.domain2.com, I have to buy another domain name called domain2.com?

If you own domain2.com you aso own abc.domain2.com and xyz.domain2.com so setting up any or all subdomains of domain2.com is just a matter of configuring DNS to point them to the right server and configuring your server to know what to do with the various requests.

Do I need 2 domain names? One for server and other for website?

No, it is not necessary to have a second, or separate domain name just for the server... use a server hostname based on your domain name -- server.mydomain.com to set-up your server. Then you may fully use mydomain.com account through your cPanel set-up.

I do not believe you need 2 domain names, you can use subdomains and even directories.

You will need 2 name servers to point your hosting account... not 2 domain name, 1 is enough.

No, this is necessary, or a different domain name server that is second only to