Welcome, and glad you could join us!
Don't know a lot, but I'll try to help in a limited way:
1. Tripod: Many types, sizes and brands available and of course, at wildly varying prices. Some of the cheap but large ones, such as the Mora one that I use only cost me $35 from Sim Lim Square. One member here once showed me an Akarui tripod/ monopod (around $90) that uses a ball head capable of handling weights of up to 4kg, which is quite sufficient for the average shooter. Your choice will depend on what your shooting habits are. For example, bird and sports photographers will use larger and heavier lenses, and hence need a sturdier support. Even a very small tripod is useful, and way better than having none at all. However, if you don't mind using railings, dustbins or ledges as support, you may be able to do without one for some time. But if you're interested in night/ long exposure photography, it is recommended that you try to get your hands on one. Others will be able to advice you better on this issue. But try not to spend too much unless you're really sure you need one, and can use it often enough to justify the cost.
2. Wide-angle lens: Not too familiar with these for a Nikon body, however I've read good things about the Tokina 12-24mm f/4. Other options would be the Sigma 10-20mm and Sigma 12-24, Tamron 11-18mm (?) and the Nikon 12-24mm. Still, use your kit lens for now and decide if you really want to go wider than that on a regular basis. For some shooters, the kit lens will probably be wide enough.
3. Macro Lens: Consider the Tamron 90mm f/2.8, Sigma 105mm f/2.8 and Sigma 150mm f/2.8. These are true macro lenses that offer a 1:1 reproduction ratio of your subject. That is to say that the image reproduces your subject at life size. As you can see, the focal lengths differ, and your choice of macro lens would depend on what you want to photograph. Flighty subjects like butterflies and dragonflies might need a longer focal length while flowers and more tolerant subjects may only need the Tamron 90mm. Besides that I've also read that it's best to pursue insect photography earlier in the day when it is cool and most insects are still resting, so it's easier to get a shot on them than when they're active later in the day, or otherwise hiding from the heat.
