1. I like making this with the long thin French baguettes which are 65cm/2 feet long with a diameter of around 5 - 6cm/2 1/2 inches. This can also be made with the fatter baguettes but the dip quantity will need to be increased by about 50%.
2. To make ahead, you can either assemble then cook when ready, OR you can bake in foil for 15 minutes per recipe, then slice it and then wrap in foil again. When ready to cook, reheat the pre-sliced baguette at 350F/180C for 5 minutes wrapped then 5 minutes unwrapped.