Next you need SSH tools on Unix or the Putty suite on windows as a terminal and file transfer tools. On windows WinSCP comes in handy as well.
I register my domains at DomainsNext.com But I think if you request it GPL Host can also register domains for you.
GPL Host can also register your SSL Certification. Just put in a support ticket for it.
Not much more to say than that. You can use VHOST feature of Tomcat to run multiple domains. If you do
remember to put everything under a ROOT folder in your war file.
There is a bit more to the setup that this so I will now tell you to read the manual for more info.