What is the best way to warm up the crepes if making them in advance?

Or if you don't have too many you could reheat them individually in your crepe pan. Probably no need to add any more butter if it's well seasoned. Just slide them a bit to make sure.

Not familiar with that specific crepe 'recipe but generally warm them wrapped or covered I foil or lidded overproif pan at 300-350F for about 10 (more or less depending on total volume). Also you may want to add a bit of liquid or fat to maintain moistness.