Funny, I'm leaving on a tour Sunday with two 32 spoke wheels (with somewhat deep section rims) and side pulls. Lightish load (30lbs), 150lbs rider. In two weeks I'll tell you how it was

Yeah 40-50lbs of gear + 170lbs rider with 32 spokes should be ok, and having stronger rims (deeper section) certainly helps. I think problems arise when you roll on bumpy, rough surfaces. Dedicated touring rides have 36 spokes, and in many cases 40 at the rear where most of the weight lies. For sure more spokes is better/stronger but you should be fine on nice roads. Of course you should carry a few spare spokes.

I believes cantis are used for tire and fender clearance. They're also very strong brakes for heavy loads. Short reach calipers are plenty strong IMO, but longer reach ones (for bigger clearances) could be a bit weaker because the longer arms flex a bit more. If you adjust them tightly you should be ok.