All insects, by definition, have six legs. You may be thinking about myriapods, which is a subphylum containing centipedes and millipedes. Centipedes have one pair of legs per segment, and millpedes have 2 pairs of legs per segment. read more
That is a good answer to your question and saves me the time to type some nose-in-the-air response. read more
In most insects the femur is the largest region of the leg; it is especially conspicuous in many insects with saltatorial legs because the typical leaping mechanism is to straighten the joint between the femur and the tibia, and the femur contains the necessary massive bipennate musculature. read more
It depends on the species. A lot of insects fly, so you could have almost any sort of leg on a flying insect, depending on what it is. A lot of flies and butterflies have, for example, cursorial-type legs while some dung beetles have fossorial forelegs and mantids and giant water bugs have raptorial forelegs. read more