Originally Posted by
DanK
If are are trying to get maximum magnification from your rig, sensor size will have no bearing on DOF because minimum working distance is independent of the sensor.
The main difference between sensors for macro work, in my opinion, is just pixel density. Given that the image size at maximum magnification is fixed, the greater the pixel density, the more pixels on the subject. For a Canon shooter like me, that makes a crop sensor camera preferable for bugs, and in fact, I just replaced my old 50D with a 7D1 (they are very cheap now) for that purpose. However, Nikons are a different story. If I am not mistaken, the pixel density of the D810 is actually a bit greater than that of the D300. If that is true (Nikonistas can weigh in as to whether it is), then there is no advantage to using the D300 in terms of image quality. A cropped image from the 810 will be slightly superior. However, there may be other considerations, such as weight.
Re lighting: this shouldn't be put off. It is extremely hard to avoid motion blur at macro distances, and the limited light in macro work with ambient lighting often means using shutter speeds that are too slow. Izzie, my suggestion is that you put off figuring out what you want for NICE lighting but that you just use a flash for now, to give you enough light and let you freeze motion. A reasonable setting for macros with a hot-shoe flash could be something like 1/125, ISO up to 400, f/13.
Macro is technically the most demanding photography I have tried. It takes a great deal of practice. I think Grahame's suggestion about how to start is right on the money.
Keep at it! It's worth the effort.