I'd run a gear calculator before making a final decision. It looks to me, for example, like there isn't a whole lot of difference between a 24-tooth chainring and a 26-tooth chaining nor between 32- and 34-teeth cogs in the rear. Based on that, I'd be tempted to stick with the stock 26-tooth chainring and install an 11-32 cassette, which shouldn't require a rear derailleur swap. If the 26-32 combo isn't low enough I'd suggest more pre-tour training, but you could always swap in the 24-tooth chainring to get a slightly lower low gear.