How long can you keep this liquer (i.e. will it work for holiday gifts) or does it need to be kept refrigerated?

To be safe, I would start your process as close to the holidays if you can (read the recipe closely, you'll need a few weeks to let it steep), but since it's made with such a high-proof alcohol, it should keep for a while -- it'd make a great gift! I'd also keep it out of direct sunlight.