ssh can be used as a VPN - you can proxy ports and tunnel all sorts of things through it. You can easily drill a connection through to say an "internal" Windows or NFS file server and grab docs off it. There is file transfer built in as well eg sftp and scp, with easy rsync integration.
It doesn't really matter whether you use ssh, RDP or whatever for remote system access but you should be aware of the capabilities of your methods and the strengths and weaknesses of them.
If your username and password are reasonably hard to guess, and ideally you use passwordless logins, and you keep your system regularly patched, and you definitely don't allow remote root logins, and you cycle your passwords say 90 days or so, then you should be fine. Do not bother changing port 22 to say 2222 or requiring 20+ char passwords. You may want to disable some of sshd's functionality if you don't use it but that might be a step too far.
Also, reset your sshd's keys occasionally and get them into your local ~/.ssh/known_hosts as soon as possible and read up and understand why ssh warns you when the keys and names look odd - that could save you a MitM attack from a bored techy in a hotel with wifi or whatever.
To sum up: a well handled sshd and client can be a fairly decent VPN and remote access solution. However, a separate VPN eg OpenVPN and then ssh over that is better and need not be inconvenient.
You pays your money .... 8)