Hi Scott
I agree with all the advice offered and would add that I don't use flash for close-up work. This is because a single flash gun will give hard shadows unless you can soften it by "bouncing" the light. Also, you'll need to be able to turn the flash intensity right down to avoid overexposure.
You can buy macro flash rings, which are designed to give soft, even light for extreme close-ups, but I've never tried one.
I think my best investment was a simple tripod so I can work with available light and use the camera's self-timer for long exposures to achieve good depth of field. I also use a simple reflector made from kitchen foil to add some "fill light".
And, of course, the beauty of digital photography is that you can practise, practise, practise without wasting any film!
Hope this helps
Rowan