I've owned an ER probably longer than anyone, though many of my fellow ER mates know much more about various aspects of the machine and Overlanding in it. I have traveled a lot but have not driven an ER internationally and I probably wouldn't, so take that into consideration. Here's my, very personal, take on the general subject of size, etc. --
Weight is your enemy on and off road. I liked hearing about Jonathan Howell's comment about being in a storm. It took me back to one afternoon where it felt like I was in a sailing ship rather than an RV. But most of the time weight means reduced mileage and compromises on harsh terrain. I've run several different sets of tires and it has only been since I got the the Continental MPT 81s and requisite air suspension that I actually liked driving the ER. Weight severely limits the tires you can use, freeway speeds, off road ability, tire availability, etc. It all depends on the compromises you want to make. The following is not really a comment on your situation but normally I tell people that unless they KNOW they want a vehicle this big and heavy as the ER they should do whatever it takes to stay under 10,000 lbs. The number of choices, everything from trails to tires, you have under 10k makes it a different world.
Exterior dimensions. Weight aside, I very often find places I can't go. Trees limit height, sometimes rocks too. In traversing a slope your height makes you wider. Width is an issue but I can easily see the widest point on the ER, I can't see the top. Surprisingly, I've never run into an off road length issue, probably because height and width already limited me ... driving around town and parking, of course, length is an issue. I occasionally have to meet people in downtown Seattle when I'm in WA with the ER. I dread it. Coil sprung ER #43 turns much tighter than the old leaf sprung ER #1 so I'm always happy about that ... truly the Ford chassis is pretty maneuverable, it's not a Sprinter but it's okay.
Interior dimensions. I have lived in the ER for over a month many times. No problems, no upper limit. With someone else I max out at a week ... but that's just me. Major Howell travels with his whole family! The ER is very comfortable for me, a load of sound recording equipment, props, and a wardrobe that covers a multitude of jobs from back woods recording to meeting with business executives. I wish it had a bigger bathroom sink. That's it.
There are places for really big off road trucks. North Africa. Australia. A great deal of North America. But a number of the places you mention on your other thread may have wide open spaces but also have medieval style cities designed in ancient times and often for defense. I feel crowded driving what we'd call a mid sized car in most of Europe. The cities are cramped, many of the country roads are small, trees, overhanging second floors, mountain switchbacks all make me like something smallish, whatever that means. You may face similar issues. I assume you don't want to completely restrict yourself to the countryside. The last thing you want to do is get stuck because of size in a crowded city where no one speaks your language. Backing up through an Indian street could be a nightmare. A recommendation, bring a bike. You can park at a distance and scout your way in closer without becoming an antisocial road blocker. The nice thing about a lot of non US locations is that there is limited suburbia so stopping outside town and walking in is an option ... I'll bet it wouldn't be uncommon to find a farmer who'd let you park over night in places where there are no formal arrangements. Farmers the world over are equipment geeks.
A big note that touches on size but covers other things too -- other cultures do not take vehicle safety as seriously as we do. They'll drive like maniacs, hook a tow from their bicycle, chase a soccer ball beneath the wheels of a backing semi. Be careful. They will risk their necks in ways we'd never consider then hold you responsible. Good visibility if you're going to be around big groups of people or in traffic ... it's a must.
My biggest issue, one that has created more trouble than anything, is too much and too complicated plumbing. I'm constantly hitting cold weather, having to blow my tanks and pipes and it's HARD to do once the weather turns on you. I was racing across the country headed back to Colorado back before we really knew the limits of what the ER could handle and froze (broke) some stuff. I stopped by ER and we fixed it and upgraded some stuff, the weather look good ... next stop LA. By the time I hit the San Luis Valley it was getting really cold again, Wolf Creek was closed ... that night it was 30 below. Diesel wouldn't flow, the hot water tank didn't like to be empty back in those days and we hadn't figured out that we should use coolant shut offs to it yet. No heat. I was so cold and shivering so hard I had to urinate over and over. It was nuts. Obviously, I broke it all again. I just turned and headed back to ER and stayed there until we'd reconfigured the whole system so it would really blow clear and so that the water heater didn't have engine heat issues ... we streamlined the diesel system with Y rather than T connectors and bigger lines. Water and Cold ... you want it simple and easy to fix.
I guess the rule is be as big and complicated as you need to be while going as small and simple as you can.
Good Luck!
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