It strikes me as odd that anyone would bother with a Canon AE-1 or a Nikon FE, much less fiddle with adapters, if they can afford and plan on using Leica lenses.
Anyway, to answer your question:
As an owner of both cameras, I find myself drooling over almost all Nikon AI manual lenses as well as AF-D primes, since they work with the auto focus Nikons and the old manual ones. I would be happy to get any Nikon manual lens, even the E series. For FD, anything Canon labelled is desirable enough for me to scoop it up off the yard sale table.
If you ask me, I would get a FE and an E series 50 f1.8, ( about $150 total retail) run through 20 or so rolls of film with prints, then decide if you like the camera/lens combo. If you find that your work suffers because of the glass quality, get some higher end Nikon stuff (and another 20 rolls), then if that doesnt do it; resell the kit and email Japan Camera hunter. He can find the most expensive equipment available.
If I had leica money, I would throw down for a Nikon F4 with the small battery pack, a 20mm f2.8, a 50mm f1.4 (1.2 if I was really loaded), an 85mm f1.8, and a 135mm f2. Throw in a nice zoom lens or two for traveling with family, a decent bag, 20 rolls of Portra 400, 20 rolls of my favorite b&w and stop reading about equipment.