There are a ton of options given those parameters. Given that you are considering a X-T20, so I assume your budget is modest.
You could go Micro 4/3s they are very well weather sealed and are generally lightweight and lenses are compact meaning it would be easy to hike with, the downside is that getting wide angle lenses is difficult.
You could also go with a Sony APS-C camera like a 6400. They are good, and can be had for cheap used. The 3rd party lens market is good and there are lots of cheap lenses.
You could get a full frame DSLR, but I think you'll find the lenses are more than you want to pay, unless you go with nikon or pentax and are okay with shooting manual lenses, which really should be fine for shooting nature type shit.
