RWS (Refined Wisdom and Spirit):
Young man there is no need to do that many exercises. In "general" I believe the ab core is one of the least understood circumference of body muscles but can be one of the most precious one seeks. IMO, the ab core should treated like you would treat your other muscles of the body, with the understanding what "type" of muscle you are working with.
When young, say for example, between 12 to 18 (males), I think its fairly safe to say that the ab core (and the entire body for that matter) are going through "traditional" development stages just through "natural" growth in accordance to genetics obtained through the mother and father.
In addition, during this time (and the times post 18), the body will respond to outside stimulus applied upon it and adapt to the stress; however, the ab core DOES NOT and WILL NOT respond "in growth"
like the other muscles of the body.
The ab core contains a circumference of "high endurance" muscles and when one considers there primary function (stablize and support, for example), it can be understood why they are. Injure one of your major muscles of the ab core, and you will find out rather quickly just how much they are in use during a normal day, I promise. Take it from someone who knows

.
I have a friend of mine (and we train together once in a while), that does weighted half-up situps, and weighted crunches, for example. I do them as well. He is progressive with the weights as I am. His abs are short and thin, mine are huge and thick. I know his work, and he knows mine. And they are very simuliar. Both of our abs have "strengthened" significantly and some growth has occurred, put it PALES in comparison to the strength obtained even with reps sub 25.
The point I am making is this: You are young, your core is going to grow at the moment because its in its development stage (I think your 18 or less, correct?), and its going to adapt to the stress applied in accordance to your training,---BUT they will NOT grow like your other muscles--primarily due the muscle composite and their primary function and purpose. In other words, it is entirely "possible" you could pound your ab core with heavy direct training (say sub 25 R) and not get the thick huge abs you desire. If you carefully do a research on some others that have trained their abs, and EARNED their so called six pack, some didnt even apply heavy weight (and their abs were thick and big), and some others have.
During my entire ab training, my "primary" progression was in strength, flexability, and squeeze. When looking through my early pics and from my own personal obversation at the time, I can honestly say that my abs (even with the MANY "months" of progressive weight training, did not get any bigger. They have always been big, and if they did grow any, it is so small I cant tell with my naked eye. Personaly, I feel I could have gotten abs without any training at all, and just let my body fat drop to show it. I just wouldnt have had the added strength, flexibility, squeeze, and to some degree endurance.
The squat and the deadlift indirectly affect the ab core and likewise will strengthen them due to the support function during the exercise. If you are doing these, your core is getting affected here.
The Ab core is ONE SHEET OF MUSCLE and DESIGNED to work in unison. Leg lifts, situps (half-ups), and leg raises---effect the entire sheet at the same time. One can maybe argue some emphasis, but the entire sheet gets worked.
The obliques are "possibly" the only muscle (when speaking about the ab core area) that will respond "more favorably" IMO to heavy weight exercises--if one wants a wider waist

eek: ).
RWS, shorten the amount of exercises you are doing to 2 to 3 (some could argue more, blah, blah). You dont need any more than about 3 exercises and vary the exercises after a certain amount of PROGRESSIVE training. Be smart in your selection and most importantly, WATCH, LOOK, AND LISTEN, to your body to learn what it responds to the most.
Best wishes to you in all the you set out to do in life and within fitness,
Chillen