Sorry I may be late to this conversation, hopefully not too late to chime in.
The DR worked well for us and we spent nearly three months in Patagonia. However, there were a few times we would have wanted something more storm worthy and you may have found it with your new TarpTent. If you take the DR, at least make sure you have plenty of guyline to tie out the apex (with Trekking Pole supports) and the pole at the half-way point. Also make sure it is seam sealed.
We used non-gore tex trail runners and had no problem beyond the expected mud and some snow at the highest pass.
You'll have to pay the $140 for the Chilean Visa. At least it last tens years, unlike others (like Boliva, which lasts the length of your Passport). Considering flights to Buenos Aires and all trips to Bolivia require the same visa fee, the only way around it is to fly into Lima and the bus down. Or walk... :)
International flights should have free baggage, even if you're going from SF to Miami to Santiago, the domestic portion should still be considered part of your international flight. To echo the above comments, you can rent or buy poles there.
I absolutely disagree with the advice not to bring water purification. Yes, if you head up to the top of the valleys and have fresh snow melt or springs, you will be fine without it. However, the majority of miles will be between the valleys (the bottom of the "W" for example) where you are long heavily trafficited areas with TONS of inexperienced backpackers and pack animals. The lower camps are crowded and may have one toilet for 30-50 campers. We saw this over and over. ANd often that one toilet will get full and you have no choice but to go in the woods. Tell me what happens when you have 50 newbie campers in a confine campsite and no toilet and one small creek running nearby. Are you going to drink that unfiltered? And don't be surprised when you find out the pack animals are allowed on all the trails and used by the workers. We found many of the workers smoking while riding to camp, even though this is explicitly illegal.
I second the recommendation to check out Erratic Rock for their daily 3pm Hike Discussion. Take their advice with a grain of salt, as they are tailoring it towards the novice backpacker. You may stay afterwards and ask questions, or hit up their knowledgeable staff. You can indeed rent or buy nearly anything you need down there. At the end of your trip, you can return your spent gas canisters for Erratic Rock for recycling (they're the only place in town that does this).
My one beef with Erratic Rock was that they told everybody to go to the local market to buy food. I did a price comparison of all the markets in town and the supermarket chain, UniMart, was the cheapest on 13 of 15 items. I'm not advocating shopping there, I just think that Erratic Rock was disingenuous about their motivations. I too like to support local. I wish they would have just told it like it is though, that it might be slightly more expensive but you're actually helping the owners and it's better for the community. But that is not so relevant to this convo. Sorry.
Hope this helps. At least it'll be on the record for the next person traveling to Patagonia.