Ah ok, lets start with the "Flies" then. I assume you will be shooting these indoors, so you don't necessarily need flash. You can use continuous light for these, as long as you set your white balance correctly. For this level of magnification, I would say the extension tubes that have been recommended should get you where you want. If you shoot them side on, you should also be able to get sufficient Depth of Field in a single shot (using a high aperture), but you may want to look up "stacking for depth of field" once you've played around with it. I assume you'll be shooting these on some kind of desk, so a table top tripod might be the best option, but there is nothing stopping you putting the camera on a book or something to begin with. That should provide enough stability to be able to test out some shots then work on the results. Yes you could get a macro rail to help here, but I started stacking shots by just pushing the book forward a touch between frames. As I say, it's better to try things out with what you've got before hunting for new kit to buy. You'll quickly understand where the issues are and then you can find the correct solutions to resolve them.
For flowers, again indoors, the setup could be similar to the above. The only difference here is that you will likely need less magnification, so you can use the shorter extension tubes, or you may not even need any. Perhaps a larger tripod would work better for you. If outdoors, then one of the big issues with shooting flowers is the wind. It's worth investigating ways to keep the subject still (google "plamp" or "DIY plamp" if you are on a strict budget). You may want to avoid flash as flowers can often look their best in natural light, or alternatively you'll want the consider some kind of large diffusion kit (again DIY if working on a budget). Depending on the "look" that you are going for, you might want to isolate the flower from the background, in which case a longer focal length lens will help blur out the background. Again, try it with what you've got first. This is the type of shot where a tripod is very useful, and finding one with very low ground clearance, or a reversible centre column would give you more options.
Water Drop Effects is a table-top setup, although a full size tripod by the side of the table should work well. With water drops you'll more than likely need flash to help freeze the action (maybe even multiple flashes). By all means give it a try, but expect lots of failed shots as timing is key. If you get really into it you can buy specialist machines that do the drops and fires the flash for you to improve your keeper rate, but these are generally quite expensive. As above try it out first and see how you like it.
Insects - there are multiple ways to shoot live insects and they range in sizes over a great range (think of the size of a Blue Whale compared to the size of a mouse, then make the blue whale twice as big and the mouse twice as small to give you an idea of range of sizes in the insect group). For most insects, flies, beetles, bugs etc. shooting in the range of 1:1 or 2:1, I find hand held shots easier to get, as they are often in difficult to reach positions and can be quite flighty. By
the time you have got your composition sorted on a tripod the subject would have moved on. That's not to say you can't use a tripod for these types of shots. Many on these forums do so very successfully, but I've always found it easier to shoot hand held in these situations. It's MUCH easier with a flash, to help freeze any movement in either the subject or the camera, but I still steady my hands against a wall, fence or anything I can lean on wherever possible. Good technique helps here, however if you are having particular issues with camera shake then holding a simple stick, touching the floor, as a make-shift monopod is also a good idea. Have a look at
@GardenersHelper thread
here for an example.
For butterflies (still an insect but generally one of the larger sized subjects) a longer focal length lens is usually helpful. This help isolate the subject from the background and means you can stay physically further away from them (they are quite flighty). a standard long lens with an extension tube to enable you to focus close up will work here. Usually flash isn't used (there are always exceptions) due to the working distance making it difficult to position/diffuse you flash, and a monopod might be more useful than a tripod to be able to quickly compose your shot before the butterfly takes flight again.
Macro rails are used to be able to "stack" multiple exposures together, while moving the focus area slightly through each frame and keeping the composition as static as possible. This is because at very high magnifications the depth of field is so thin as to make a single frame unusable. Stacking several (often 10s or 100s) of images together creates your final result, with the whole subject in focus. Typically rails are used for high magnification studio shots of dead insects. Although you will encounter this at some point in your journey, I'd suggest leaving it to one side for now as this requires additional software and processing techniques. When you get to a point where you want to try it out, cheap rails can be found for about £10 on ebay, but as with most things you get what you pay for and should look to get the best you can for your budget.
Hope this is useful to you and gives you enough to mull over. The key message here is to try it out with what you have before looking to buy new kit. If on a budget it's better to prioritise what you do need rather than buying stuff you may not use that often, or can do without.
