...the tire clearance issue is a real concern. Ive toured a lot on 28 slicks fully loaded and it works fine, but like the case of the friends bike that with 25mm tires and caliper brakes like this bike, she has about 3mm max clearance, and in fact she came to me with the problem of a tire rubbing--it was simply that the brake had been moved over and was slightly loose, so the spring was pulling it to one side, rubbing the tire. She plans to do a trip also, but the fact is, if she busts a spoke her wheel will go out of true, and her brakes dont even have those little release things, so she will really be out of luck with a rubbing tire when and if it goes out of true (same idea, load only on rear wheel)
frames like this with caliper roadie brakes do have limitations, and why often a good hybrid with v brakes or cantis and lower gearing overall make a good bike to try touring on, and nearly always with much more room for wider tires/fenders/wobbly wheels not hitting frame or brakes.
just stuff to be aware of, this is what the fellow is asking, the details.
I'd expect the OP to check clearance
everywhere, including under the brake caliper. I agree that a hybrid (or a touring bike like the Windsor above) is a better choice if the OP can't pare his weight considerably. A good reason for N+1.
Brad