Okay, this is a good place to start. I suggest you think about how much time you have available, then where you want to finish.
You can then decide where to start. Depending on your daily mileage allowing for rest days you should be able to calculate this so as to start from somewhere easy to reach.
There are other options than trikes. You can hire a little donkey cart in France bourricot.com will help here, look for randoline. They require a helper to lead the donkey, you don't get to steer, as they are made specifically for people with a disability. You might want a tandem bike, or maybe an ebike. There are also options to book with companies that will arrange accommodation and baggage transfer.
You could buy a trike (try cyclo-eko in Pau, who sell a folding trike with electric assist) and sell or donate it when you have done what you want with it.
Your friends will need to work out what they want to do, as well. You might decide to use an assist vehicle, but that would exclude them (not you, if you are disabled) from some accommodation.
You may want to do a test run if you have a locally available walking route.
I suggest a good think about your objectives and ability to ride on a regular basis before coming to a decision. Remember that transport costs from the USA will be a very large part of your budget, and the others will need to be willing to move at your pace. Don't worry about path width. There is always an alternative route. It's not an obligation to follow the track markers.
Hope this helps. It's just a few ideas to help you research.