the goal is a expedition build to travel around South America, the US, Canada.....
I drove my stock TJ from Alaska to Argentina, and kept a keen eye for Jeep dealerships/parts/etc., so I can chime in on the "Jeep parts availability bit".
Checkout this page to see where Jeep has official dealerships. I have to imagine an official dealership can order you anything you might need.
http://www.jeep.com/crossbrand/intl_site_locator/index.html
Basically, there is an official Jeep dealership in every single country, and many small mechanic shops will have or can get suitable consumables.
I had no problem getting oil & air filters in Mexico, Panama, Colombia & Argentina. I was also interested to see they had things like headlights, serpentine belts, etc.
Of course, the biggest difference is that every Mechanico on the side of the road knows how to fix a Toyota, and probably knows of one nearby he can pull parts off.
With the Jeep, you might find people are not as familiar with it, and so you'll wait / or have to pay bigger bucks for service at a real dealership.
Personally, I always figured if I got in a real bind, I'd have my brother buy the part in North America and ship it to me, and I'd wait beach-side for a few weeks until it came.
No big deal.
In summary, driving the Jeep will put you at a disadvantage for parts/service, but I wouldn't let that sway you.
-Dan
It's anecdotal, but my TJ made the 40,000 miles without a single issue. Nothing more than flat tires (nails) and oil changes.