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The Egg is awesome, I think you are making the right choice with the large.
My biggest piece of advice is to calibrate the thermometer when you get it before you ever cook. No one told me to do that and I had a lot of frustrations before I found this forum and even knew that was a possibility.
Second piece of advice is to tell you that they suggest that you cook at or below 400 for the first several cooks to help protect the gasket, and that if you ever do really hot temps with the platesetter in (like pizza), you should keep the legs up on the platesetter to avoid diffusing the heat right at gasket level.
Third piece of advice is that at some point you will enjoy getting an instant read meat thermometer like the thermopen, to keep you from over or undercooking smaller pieces of meat, and some sort of temperature probe thermometer with an external display like the maverick 732 so you know when to take those boston butts / briskets off. But those things can wait a bit. JUST MAKE SURE YOU CALIBRATE YOUR THERMOMETER - takes 5-10 minutes and my thermometer was off almost 100 degrees.