F-stop 2.8 is good, but 3.5 will work. With every decreasing f-stop you loose depth of field and have to use a longer exposure, which leads to increased risk of blurred images. The true macro is characterized by its ability to focus at very short distances - down to 5 centimeters or a couple of inches. This means that the object photographed can become very large on the film. To obtain this you will probably have to buy extension ring for your macro.
Most compact cameras lack a sufficient macro capacity for fly photography.
The extension rings can be an inexpensive way to convert a normal lens to a macro. All the ring does is move the lens away from the film plane, leading to a greater enlargement of the subject and closer focus range. The rings are fairly inexpensive, and can usually transfer all functions including auto focus and aperture control. Another alternative solution is a reversing ring, which you screw on the front of the lens. It facilitates turning the lens, mounting it backward on the camera, which, particularly enough, will give you a fine macro lens.