Abs are one muscle, its impossible to isolate lower abs. Diet will be what will have you're lower abs going.
Pretty much... I mostly use regular crunches, reverse crunches (on an incline), roman chair crunches and occasionally hanging crunches (not leg raises, but where you curl your back and make a crunching motion). Sometimes I incorporate twisting motions to hit my obliques, but for obliques I mostly rely on standing side twists (very good for obliques). Then I do DB pullovers for serratus. All of this will get you where you need/want to be development wise; the rest comes from dieting to get lean.
Any abs-specific exercise will involve rounding of the lower back and you bringing your sternum towards your pelvis. Exercises such as leg raises may be beneficial, but you're working the hip flexors primarily here.
When you're working abs your movements should be controlled and deliberate. When you crunch, squeeze the muscle rather than just being fast and choppy. After each set of abs try doing some stomach vacuums... Just try it and you'll see why I recommend it.
Abs are talked about way, way too much in my opinion. Everyone wants good abs but few realize how easy they are to develop; it just takes dedicated, smart, consistent work. The hard part is dieting to the point where they're visible enough to your liking.
Good luck brotha