hi christine -- sounds like a great trip! the chalten massif is gorgeous, and whether backpacking, climbing, or both, i bet you'll love it. just unbelievably spectacular.
tent -- yeah, 3-season should be fine for that. i spent a few weeks in one at de agostini camp several years ago, and many others have as well. at those camps, you're in the trees and in the rain shadow of the massif, so you get this interesting thing of super mild conditions mostly -- it's mid-summer there, of course -- but with an alternating mix every 30 seconds of sun, rain, and blowing mist. definitely bring a hard shell!
if you spend any time in town, there are hostels and at some of them you can camp in their yard for less than the normal hostel fees.
i've only climbed a couple of routes there myself, but one was the amy on guillaumet, and it's largely a mixed route, i'd say. you start with an ice couloir (easy, like 70 degrees max), but then the rock climbing above, which is easy (maybe 5.8/9?), is stuff that i think most people climb in their boots. things like the sportiva trango S are ideal -- stuff that takes a crampon, but also climbs rock pretty well and is nice to hike in. you have some snow climbing above the rock in order to summit. but it's really a terrific route.
i can't remember the rate for the bus, but there are links on rolando garibotti's site: he has links to the busses here: pataclimb.com/knowledge/res…
exchanging money is kinda interesting there. inflation is crazy, like 25% yearly or so. the official exchange rate, like from an atm machine, vs what you can get on the black market is hugely different. in my experience, the black market isn't something sketchy, like follow guido to a dark alley, but something that works ok if you ask around a bit. can save yourself a lot of money.
if you haven't checked it out, for climbing rolo's site is *the* source (as is his guidebook, which is gorgeous). he knows more about the massif than anybody in the world, and has good info on his website: pataclimb.com/
his route info isn't hand-holding style, though, just fyi. his info definitely assumes a certain level of alpine expertise, i'd say, and the ratings aren't boulder canyon style :).
last time we were there, we spent the night in el calafate at a nice hostel (forgot the name, but i could probably find it), bought a few groceries in town, but that's not really necessary b/c you can get all you need in el chalten, it's just more expensive.
anyway, i hope this helps, and have a great trip!
kelly