Looks like you've got most of it, Pepper. Of course, there's always more things to get, it's the nature of the hobby. Are you getting the deluxe caliber conversion, so you have a powder measure on each toolhead? That's how I have mine set up, really cuts down on time for caliber changes. You should definitely have loading manuals, and have an idea of what kind of loads your are looking for.
I'm in PDX, let me know if you need a hand setting up. I've been running my 550 for about 20 years now, so I think I've worked the bugs out pretty good by now.
Remember, Murphy always wants to visit with the inattentive loader
