I would do a couple of tests. I would try to take a few pictures zoomed out with the camera as close to the food as possible. I would compare those with some where you are zoomed in and move the camera back.
As for the best ISO, you generally want the lowest possible ISO that will still give you a shutter speed that is "fast enough." If you use a tripod, just use the lowest ISO. If you are hand-holding, try for a shutter speed of 1/150 or better.
Again, do some experiments. Shots with a higher ISO will have more noise (little colored dots). Shots with a lower ISO will have a longer shutter speed with means that they will tend to look blurrier. That's because the longer the shutter is open, the more likely you are to move the camera a little during the shot.
You can help things out by having more light. Put your food in a brightly lit area for the best results. A great idea would be to put it near a window receiving bright, indirect sunlight. Then put a white board on the other side of the food (just outside your picture) to reflect even more light back onto the food.