mikkekeswick, I'm going to contradict you here...sorry. I wouldn't recommend sanding this fine. first off, it's not necessary. If you were staining wood, a fine grit is advantageous but since you covering with a clear coat, you won't be able to see any of the scratches above 180-220 grit unless they are badly swirled. Also not knowing what finish you intend on using, a 320 won't give it much to hold on to.
Now between coats, I do use 320 but I rarely sand past 180 before finish.
Now if you are doing a oil finish, all I mentioned is mute.
BigJim