I went back and looked at some of your "plane" and your geo. If you were the same one asking about an extrusion issue and having multiple faces then that may be your problem. If you didn't go back and clean up or even reset your extrusions then your geo is going to be a nightmare. Check your number of extrusions again and they should be at one unless you have them intentionally changed to something else. It's a common problem, at least for myself to remember to reset them after multiple extrusions. For your selection issue tumble your camera some or dolly in close enough to select one face, actually have one piece of geo on your monitor and select it, if it still selects multiple faces then someone on here can maybe fix that issue but I've personally never seen it before.