Welcome to APUG. My advice is use the lens you've got. That lens should be capable enough for what you have in mind. Nikon made a few different versions over the years, and I had one which I took to Costa Rica and Panama. It's very light, which is nice when traveling! Also, as it's not that expensive, I wasn't too worried about what might happen to it in the rain forest.
Don't worry so much about how sharp or fast it is and just go take photographs. When you find that the equipment limits you, *then* start thinking about what equipment will produce the results you need/want. I say this as someone who learned the "it's not the camera/lens, it's the photographer" lesson after buying a lot of unnecessary stuff.
Try a lot of different films. When you get something you like, use that film more. There are plenty of threads here discussing film choice.
EXAMPLE: bigger or faster is not always better. I used to have Nikon's fabulous and seriously pricey 70-200mm f/2.8 VR lens. It was great but heavy and didn't focus nearly as close as I'd like - the close focus distance is 5 feet. I sold it and bought an older, much cheaper, Nikon 70-210mm f/4 which is slower and technically nowhere near as sophisticated, but focuses as close as about 3.5 feet. It also weighs a lot less.