If you're going to use downtube friction shifters, suddenly your life becomes a lot easier, because they don't care what freehub you use (Shimano or Campagnolo), and they don't care how many speeds, 7-8-9-10-11.
However, you'll find anything above 9 speed is much more "finicky" when hunting for the gear you want... so I'd suggest considering 9 or 8 speed with friction shifting. Just set your limits to the bounds of the cassette, and shift away!
Do make sure the overall range will be covered by the shifters you choose. Older shifters have a smaller diameter and pull less cable, having less range. Stuff from the mid-80s upward seem to work just fine.
As previously mentioned, cold-setting to 130mm (esp from 126) should not be any problem.
Any bottom bracket you want should also be fine, as long as it's Italian. I just put an external cup Ultra-Torque on an old Colnago, taking a square-taper out of it, all Italian threads. Italian bottom brackets are not hard to find, and so you won't have any problem putting whatever crankset you want on it. I like to stay within brand here, as far as bottom bracket + crankset; and obviously use a double crankset with the correct bottom bracket. I thought doubles were 102mm, but I'm not expert here, so double-check that.
I'd be surprised if most any front derailleur couldn't be made to work also, as long as it's double or triple -specific as you want. Again, since we're friction shifting here, your "margin of error" is quite large, and you just need to set the limits.