Several people advised getting my expansion done or at least roughed in) before engaging with Tesla; and, Tesla has been really uncommunicative, which is kinda scary. Obviously the people who responded know more than I do, so I'm taking the advice: I cancelled the order, and I'll get my house more in order before I tackle backup systems. (Cancelling was really easy, even though I'm well past the "5 days" their Purchase Agreement mentions.) Thanks for coaching me, and I hope y'all will still be around and as helpful when I try again!