If you want to build your system just for spot monitor purpose, I recommend to use usb dongle type device which is directly connected to HDMI on your TV.
I am using it on my shop, and ip cameras(ONVIF supported) are linked to the device wired/wireless. It pretty works well on my shop. However recording is not supporting with the device. Previously I used bulky decoders and screen quality is better than usb dongle, but I am satisfied with its mobility and I am able to watch multiple channel of screen as compared to decoder. usb dongle type could be suitable for your system. name is "ipvista". you can google it.