Hikvision makes the cameras for many other brands. They default to serving their web UI on port 80. It's probably getting roped into your reverse DNS somehow.
Try the default Hikvision login admin, 12345/admin to see if you can change the UI port
As others have said. 150 watts at idle is going to add around $30/month to your power bill. A proper NAS is around 30 watts at idle with the drives still spinning. A media server is an investment in convenience. Definitely spend a bit more on the hardware to save over the lifetime of the server.
I use a Dell R210 mk2 with quieter fans. It idles around 15 watts and can handle transcoding tasks when needed.
I also wouldn't recommend Plex. Go with Jellyfin instead. Much less headache.
You can mount ears to the middle and rear of the chassis, but as everyone else has said use the rails.
The HP Z600 is good value for money. Units a few years old can be bought cheaply. They're quiet for the compute power on offer. There are hundreds of different configurations available all the time on eBay.