Hi sbbasile,
I have sent you a Private message to cover this question and your previous question. Unfortunately the translation between the referenced links and French will prove to be a difficulty.
The TV size and brand depends on your requirement. If you want a screen larger than the largest monitor then go for TVs. What is more important is the resolution. Cost will also be the significant factor. If you can get 3 screens for what you have to spend I suggest going for the TVsX-Plane has been significantly changed the best resolution at this stage is 1920 x 1080. X-Plane is not known to work too well with 4K resolution.
I am running the same graphics card and will be running 3 43 inch TVs off the card. In the video links I have given you in the private message, Russ Barlow has connected 3 49 inch screens to run his configuration.
Good luck,
Glenn