StirBlue and Corinne, is my guess correct that you haven't eaten Reubens before? I'd think if you had you'd feel comfortable guessing both on quantities and procedure, but maybe I'm wrong. Anyways, here are both according to this reuben lover!
Bread? Two slices
Corned beef? Enough to cover one slice of the bread generously
Sauerkraut? About equal with the beef
Cheese? Enough so that when it melts it will cover the sauerkraut
Cream cheese? Non-traditional, but why not? As much as you wish!
Thousand Island Dressing? Enough that its presence is noticeable, even with the other strong flavors within. It's an important 'flavor note'
Black pepper and (yes!) caraway seed? To taste. Plenty, in my book.
Procedure? Get the one slice of bread and start piling on. Maybe start with the dressing so that it will easily stick, smearing in the cream cheese then as well if you go for it.
Then put on the corned beef and cover it with sauerkraut and the sauerkraut with the cheese, then grind your pepper and sprinkle your seeds. Top with the other piece of bread, squoosh it all down a bit with the palm of your hand, plunk it in the crock pot.
Mind you, a grill or frypan would brown the bread which I'd consider a plus, but surely the crockpot will accomplish something good too. For me it would take too long as I'd be salivating from the moment I cracked open the sauerkraut!
Accompany with a CHOCOLATE EGG CREAM!