how good will the wireless signal be is the question and you have no way of knowing without trying it. For what it's worth, I have the same product in my house and tried it from down stairs and it worked but I have a modern place.
Probably, as this is exactly what they are for. So long as the RF signal can get through your walls and the receiver is within range (although you can add a signal booster) it should be fine. Can't seem to find out what the range is exactly as it depends on many things.
Hello.. yes,.. that is exactly possible. Having purchased a lot of the devices, it is my routine to simply turn off all the main lights around the house from the bed. There is no need to go into each room turning them all off and stumbling in the dark to the bedroom. With the internet controller, I can choose do it from the RFLightwave App.. where I have an option to turn every device off at the press of one button, or the wireless controller.