The external switch i use is the standard wall light switch. I don’t think a momentary switch would work. You can use thin wire since S1 & S2 on the mini is only 3.3volts.
You can install the companion smartapp from the bottom of the step by step post. It is not a instant status update but rather 1 minute polling. Knowing that the status will be up to date in 1 minute is fine with me.