Making my own server...

Accessing it externally largely depends on what services your NAS (Network Attached Storage) offers and on what ports; Secondly, what your ISP filters may be an issue as well.

For instance, many NAS devices have a web (http, port 80) service. You can open port 80 on your firewall, but many ISPs intentionally block inbound port 80 because it prevents people from running home web servers.

The same goes for SMB/CIFS ports, which IIRC are 137-139. Plus, it would be a pretty bad idea to blindly open SMB/CIFS and rely on it's own username/password that can be easily found.

Arguably, a dang good way to connect to your home network securely is using SSH tunneling. It requires that you familiarize yourself with the command line and the ideas of encrypted traffic. You would also need to have a server accepting SSH connections at home (hint, your mac works - Turn on "Remote Login")

Personally, all my inbound ports except for SSH are refused at the router. If I went to access files, or access the desktop of one of my home machines, etc, I just 'tunnel' traffic to the applicable port. It's essentially a "poor man's VPN" but it works really well for me.