Keep in mind that QFinder is not required, ever. Once you’ve reset your NAS, it will default to DHCP addressing. You can look in your DHCP server information (usually your router) and find the IP address. You can then simply use a browser and the IP to access the admin GUI.
Personally, I would not expose the NAS directly to the internet (for inbound connections, no issue with outbound), then you can leave the Admin user enabled as there are a number of things that still won’t work correctly with it disabled.
Once you have access, you can also set a static IP and/or an IP reservation in your DHCP server. This avoid all sorts of other headaches down the road.