Hi,
The removable plates are on the newer 'next generation models'.
Other than that the model to get would depend on what or how much you would wish to cook at anyone time. Mine is probably in the region of 10 inches by 12 inches. Can't measure it at the moment cause I'm at work and it's at home. But that will adequate cook a meal for one, as in a chicken breast/chop/steak and veggies for one. Or a couple of steaks etc.
Their are of course the ones that work as griddle as well, but it would all depend on what you would use it for.
In terms of cooking, try to get everything a similar thickness. The plates need to be in contact on both sides in order to cook things properly. And don't be afraid to start something and add other items later, cooking times may be shorter for everything, but they will not change relative to each other. Finally, tomatoes on George are lovely, but very sticky and prove difficult to clean off if left on too long (either in cooking or afterwards) hence removable plates ome in.