A 550 will go farther than a 6000 which will in turn go farther than a 7X. The 6000 is the fastest of the bunch. Most 550s have the galley in the back between the passenger lavatory and the passenger cabin while the 6000s have the galley forward by the boarding door. I'm not that familiar with the 7x. There are more used 550s out there for purchase and more type rated 550 pilots than on other 2 so it would probably be easier to get and easier to crew. As far as cabin lay out goes, they will all probably be arranged in 3 separate passenger zones. There is an almost infinite amount of configurations available for the passenger area, but most common will have a state room with a couch that converts into a bed along with 2 seats opposite that face each other. There will also most likely be center section with either 4 seats club style with a table between and a credenza opposite them or 2 more seats instead of the credenza that allows for a table that seats 3 per side in flight for meals or conferences. The forward passenger section will most likely have 4 seats in a club configuration. Another thing you will want to think about is internet capability and CPDLC already installed. You will most likely want KA band internet and that is not cheap to install and it is also very expensive to use. That said, business now almost always demands high speed internet at all times and if that is needed, it must be accounted for beforehand. Good luck.