First of all, We recommend the use of monitors so that you have greater control over your network and not run the risk of someone from the establishment modifying the television input and moving from showing the programming of your playlist to showing something recognized in the other inputs of the TV.
For more information about the difference between monitors and televisions, we suggest reading the article: What do I need to know about the hardware?.
Regarding the size of the screen, this is very important to avoid inconveniencing the personnel who will observe it.
The screen size varies according to the distance from the screen to the public.
There are some recommendations regarding the distance from the screen and its size, however we suggest that you do a local test to see if the contents are available and look good.