RE clamp size: I've never had a problem using a regular 28.6mm FD on any French bike. It's close enough. There's probably an exception to this somewhere but I've never run into it.
More important question is: what derailleurs to put on it? Huret Allvit? That would be a statement of sorts.
100mm front hub should be fine. Did you measure it at 96? Best to check dropout alignment if you can.