In short. If you buy a display console , yes .. you need to add all the sensors to it (rather easy actually, usually). They are separate devices . But, you don't need the display console to send out unless you want it to. So no, it won't duplicate data on Ecowitt.net, unless you have the new console send to it. And you do not need to have it send out to Ecowit.net for the display console to work.
Another option, is to buy a cheap tablet , and just have it display the webpage from the device or Ecowitt.net ( there are a lot of different options here, the tablet could actually use other methods to view your data, etc, but I'm keeping it simple) . Other words, the tablet would act like your phone and display the same thing, yet you use it as a static display, and mount it somewhere
Others are going to chime in with more complicated options, templates on how you want the data, and a lot depends on your skill set. I'm just giving simple answers to your questions.
Edit: What I mean by using a tablet in the most simplest sense , as all you would have it do is display the web page, all the time. You would need to change the settings on the tablet to not go to sleep, or turn off the display (simple actually). I use the same method to have a permanent display of my security cameras which is also a web page.
