If I wanted to make these for Christmas dinner and I was prepping ahead, do you think I could boil the potatoes and flatten them, but then refrige...

You can definitely boil the potatoes in advance. Flattening might work too, although that's easy to do just before frying, and might prevent them from getting breaking apart.

How many people are you serving? I love this recipe, but the only thing to keep in mind is that you can only crisp so many in a pan at once. I think they would hold well in a warm oven for an hour or two before dinner, if you don't want to get stuck at the stove.