most likely that crank will be able to take easily a 24t, maybe even a 22t, so keep it in mind if (and perhaps when) you find you'd like a bit lower gearing. A 24t granny can be found for probably under $20 and its a super easy change, and most likely again you wouldnt have to touch the front derailleur, it would just work right off. Having ridden with a 19.5 gear inch low gear in pretty steep areas, I'd recommend making the switch, it wont affect your riding at all, but essentially it will give you one lower gear than what you have now. You'll be packing a good amount for a trip like this, so its entirely normal to want to have some lower gearing than the 28-34 combo.

take a peek at the Sheldon Brown gear calculator, put in your wheel size, put "gear units" to "gear inches", then find your 11-34 9 speed cassette and it will show you your gearing in "gear inches".

Sheldon Brown's Bicycle Gear Calculator

Neat to see an actual number for your gearing, I've toured in hilly areas a fair amount, and in Latin America steepness of hills can be quite a lot steeper than in N America on the whole, so for me getting your low gear down a notch is a win-win, you might not use it often, but you'll be glad as heck for it sometimes.

Like I said, if you dont do this now, any bike store along the route will have reasonably priced 24 and 22 grannys. Takes just a few mins to change it out.
Will follow your trip on CG if I remember.