I would plan on getting the bike and riding it for a time to see what your needs are. You may find it needs nothing for the way you use it. After all it's a great bike. I'd put good gear and comfort items first and then add other stuff as needed. Some Roc straps and a Dry Bag work well for that once a year big trip.
Shop for a bike that is well farkle, and remember these bikes will run for a long time if maintained (get the paperwork). So a bike with 25k or more miles is just starting to run in.
For me a non factory exhaust system would be very far down on any list I made, less mpg, more sound and less low end, but very cool looking !