"I will encounter mostly tropical weather the rest of the time."
I'd focus on this and look at your cold weather stuff for when you get to Patagonia or wherever it is you're going in southern South America.
For the tropics…
Again, a lightweight $30 40* synthetic sleeping bag from Walmart/Big5 will serve you well. I'd recommend not overthinking this one. If this is an extended trip, you'll have a better idea of what you need for the colder climates once you make your way to southern Chile/Argentina.
You really need to look at a tarp. I sat out some monsoon rain under a USGI poncho which is roughly 5×7 or something like that. An 8×11 tarp will be a palace. You don't need a PhD to figure out site selection and not to pitch the tarp over a bowl where the water will collect under you. Invest a minimal amount of time learning how to pitch it with cordage. For my entire time in Panama, I never not once ever ever ever never ever used trekking poles or stakes. Cordage or bungee cords 100% of the time tied off to trees and deadfall in every case and we’re talking well over 100 nights in the jungle. I'd bring stakes for convenience now though but certainly not necessary. Pair this up with a Serenity Shelter from MLD and you'll be set with a shelter that's a lb (or not much more). Bring some trekking poles or UL tent poles and you can pitch your tarp in a clearing when trip/traveling companions dictate.
It really doesn't take much beyond that first leap of faith to get out of tents and into tarps. While I have a really nice tent from Zpacks, my next shelter is going to be an 8×11 tarp as I really miss the simplicity of it and feeling so connected with the wild.
http://www.mountainlaureldesigns.com/shop/product_info.php?cPath=21&products_id=120
If you're primarily going to be in the tropics, ditch the white gas. I'd suggest it MAYBE if you'd be melting a ton of snow but not for tropical camping. I'd buy a stove from Jon at Flat Cat gear which burns rubbing alcohol called the iso clean stove
http://flatcatgear.com/page13.php
While I'd normally prefer a stove which burns denatured alcohol stove (actually prefer Esbit over alky stoves at all), the beauty of using rubbing alcohol is its availability as you travel. Stop by the first drug store as you enter the country and you're done. One caveat is that once dry season hits, go to a no-cook diet and bury whatever stove you have at the bottom of your pack. Watching Kuna (elephant) grass burn out of control is not a fun experience. Wouldn't want to be personally responsible for burning down a village.
Edit: So I'm a liar and just bought a 9x7x5 Grace Solo off of gear swap.

