And here I go. I said I wasn't going to comment, but since you asked . . . 🙂

I think you'd need to have an extremely high degree of confidence in that small data center - at the end of the day, it's still a third party you have to depend on. With your home backup, you're looking good. Please, don't get me wrong, everything can still go wrong even if you've got it all on your own premises, but the more autonomous the witnesses are, and the more spread out they are, the less importance any one failure has to the entire ecosystem (and, of course, that failure is recognized, accounted for, and recovered from). The key idea I want to impress on everyone is that the more we are setup in that direction, the better, and the more we depend on "cloud" infrastructure, the worse. It sounds like you are somewhere in between, leaning towards complete autonomy - I even get the impression that you have a personal face-to-face relationship with that small data center (for those who don't know, don't laugh, I've worked personally with small data centers - they do exist).

Thanks for the question, but hopefully no more comments from me if I can help it. I really prefer to have more knowledgeable and expert people responding to these kinds of questions, if possible.