Just bought 3 additions units (AC1200) and want to preprogram them prior to taking to another home that i own. Can i add them to my existing wifi network in my primary house and just take them over to my other house and hook them up to the modem and use them without any additional modifications. My primary home devices currently use the same Wifi name and PW as my other home. so i am hopeful that it will be transparent. Or do i have to do the setting up at the other house.
That would not work. You must set them up in a new Google Home home, and you should do it when at the other place.
Then you decide what network name (SSID) and password to use, so just reuse whatever you already have.
You could add them to your existing network at home just to get them updated, but then do factory reset them afterwards before taking them with you to your other place.