A. You probably just need one. You can choose according to your requirements between a single channel or multi channel remote control. The remote control's emission frequency is 433.90 MHz and the emission distance is 200m for outdoors and 35m for indoors, so we advise if your house is quite large (2 storied house) and have many rooms, it's better to use two remote controls (emitter) which you can use for each level.
You can have as many as you like for your own convenience.