keep in mind temperature reports, will you be staying in high altitude which can have vastly different weather than sea level in those countries.

I traveled costa rica for 3 weeks, and backpacked for 4 days in the jungle during that trip.

buy everything before your trip imo. very difficult to get things in costa rica as their roads/delivery infrastructure was crap. easier and cheaper to buy in the usa.

are you carrying your whole trip load while going through the outdoors? or will you leave your non outdoors stuff elsewhere. If you'e carrying everything I think youll need a big backpack, 85l minimum. I would buy everything then pre pack to make sure it figts.

there are certain you get cold in the outdoors. when you're not moving eg breaks, lunch, camp evenings and when you're sleeping. you need the to know what kinds of temp lows you'll face at night. You need enough insulation to sleep comfortable. I'm a cold sleeper, so in 32f nights are cold for me. I need a 32f comfort rated bag (or 15 degree "normal" rated one) + thin sweater + thick fleece sweater + fleece balaclava + pants + socks. I'd buy most of that gear on amazon.