I'd definitely start with Bike Friday. In addition to (IMO) making the best bikes for touring, they also do a lot more customer outreach along the lines of what you're talking about. Almost all the parts are standard.

I believe the best outcome in this respect is an arrangement similar to Pactour -- e.g. http://www.bikefriday.com/desertcamp Keep in mind, though, that the owners / operators of Pactour have both a reputation and a long-standing relationship with BF.

You might also want to talk to Xootr Swift about something like this. I don't view them as the optimal choice, but they are both big enough to consider doing something, and small enough that they are less likely to blow you off.

Aptitude for climbing depends almost exclusively on the gearing; you tell BF you want gearing appropriate for a tour, and you've got it. (Swift would need some customization, which would be done by the LBS or cyclist.) The handling is more responsive, though, so descending is a little trickier.

Maintenance is the same. I'd stock some 406 and 451 tires and tubes though, as they might be a little harder to find in some areas.

For planes, folding bikes are easier to pack than standard bikes and almost always avoid the fees. However, your clients will likely put their bikes into hard-shell cases, and will almost certainly ask you to store the case for them during their tour.

Re: other transport, folding bikes can usually avoid the extra fees. E.g. Belgium normally charges €6 to take a bike on a train, but no charge for a folded bike. Not sure about France, you probably still have to bag it.