A 24 speed makes sense. Anything more I wouldn't worry. Your'e obviously doing your homework, look at Bikefriday for portabiity. Read the Rivendel site. There is lots of stuff here.

At one point you mentioned building your own: What about this: http://fellini.net/lht/

Partability and ability to take it on a plane seem to be part of your mix, and that will determine quite a bit what kind of bike you can go for. You cna pay quite a few shipping charges before the air upcharge gets you back in the money had you bought an expensive compactible bike.

When it comes to weight, as you know, rotating weight is what you want to avoid. And rotating resistances. So wheels are the big issue. particularly if you end up with 26" stuff, make sure the rims and everything are as light a possible, be sure to have high pressure tires, of the smallest practical width, but no smaller than what you need. So for instance I went to 37mm because I had a lot of loose trails in the mountains, with everything else being paved. But normally I prefer 32. I always get zero tread. But while the wheels need to be light, you need good puncture proofness, and great tough spokes. They need to be touring wheels. F

rame weight is probably at the margin a few pounds. Groupo weight isn't the issue, you don't need the lightest stuff, cause it isn't built all that tough, and may not be available for the widest gear range.

You do need to go light, but there can be a few things you go over on. Like the frame, you can save 1 grand there, and possibly save some weight if you could drop the S&S stuff. But either way, there are reasons for going over there. The key thing is to have a weight budget, and not go over everywhere.