Oracle Database Remote Connection
Your connection string is wrong. With easy connect you need to provide a hostname and servicename/SID. In your case you would provide
sqlplus user/"SomePass"@HOSTNAME:$PORT/servicename

If you want to configure your connection in the tnsnames.ora, you can connect to it using sqlplus user/"SomePass"@TNSALIAS

I actually don't understand the part of your question with your local Oracle XE installation. If you only want to connect to a remote database, you don't need it. All you need is an oracle Client (Instant Client with sqlplus will do fine), or a tool like SQLDeveloper. If you are unfamiliar with Database administration a tool like SQLDeveloper might make life a little bit easier.