Discs can be fine, but I don't think mixing brake types is a great plan. It's more complex than necessary with minimal payoff.
• Disc and canti will brake at different rates. That would drive me nuts, and could also be potentially unsafe.
disc and cantis use different lever types. So you'd either need to use one travel agent (suckage) or two different brake levers (also suckage).
• Unless I'm missing something, you should be applying even braking pressure to the front and rear - especially when the bike is loaded.
• Field service on disc brake is more difficult than cantis; and two braking systems means you'd have to be prepared for twice as many potential brake repair issues.
And while rim problems do happen, proper braking technique and maintenance ought to mitigate most issues.
In this case, I'd just stick with cantis.