Is it ok to freeze buttermilk?

I agree with the above. There's always more buttermilk in the carton than you need for a recipe. I like using buttermilk in a potato salad instead of mayonnaise when I have extra. You can also make a salad dressing with it for a green salad and I love bran muffins with buttermilk.

Depends on what you'll be using it for. Once frozen it breaks and develops a grainy texture. Not noticeable when put in baked goods/pancakes, but very noticeable in things like pudding or sauces or candy.

Alternatively, make biscuits from what you have and freeze them.

Yes. But only use it for baking.
You can also find powdered butter milk in the supermarket near the powdered milk, baking section to mix up just a bit for baking. It doesn't have the fat tho, so YMMV for the application.