2) My ab philosophy is train them with heavy resistance or body weight exercises that add a lot of resistance. I typically do 2 sometimes 3 sets of straight leg drawbridges on an incline pulling everything but my upper back off of the bench then lowering my body slowly. I hit about 10-15 on first set and then how ever many I can do on the subsequent sets. Then I will finish them with 2 sets of crunches to failure. If not drawbridges then I work with weighted resistance like cable crunches or machine crunches with heavy weight. However I feel that most of the ab development comes from stabilizing and supporting the body in other heavier lifts like squatting and dead lifting. I do something for my core 2-3 times a week after cardio. If not a direct ab day then I do dumbbell side bends with like 50 lbs weight on once side only and slide my arm down to touch my knee. I do 2 sets of 20 of these and my whole core is worked. I will do them leaning back a little to hit the abs, then leaning forward a little to get the erectors and rear side of the obliques.
3)In general the 2-1-2 is the pause during the resting portion. On say bench and pressing movements this would be lockout. With a pulling movement it would be at the point extension though and not at the bottom where a sqeeze of the contraction can take place. The real idea behind the 1 is to point out I am coming to a complete stop. Not always for a full second but enough to take the rubberband snapping back effect out of the lift. It is also there for me to take longer than 1 second on occasion when I need to take another breathe or to before trying to get the next rep in good form. So say on a squat I may stand with the weight for 3-5 seconds catching my breathe before descending into the next rep.
I think the squeezing of the contraction is great for trying to pull out separation. However as far as it having any true muscle building effect there is not one that I know of unless it would be increasing the pump. However the focus of this is a continuous weight progression to cause growth. That being the focus there is not a lot of wasted energy on intricacies. I make an effort to keep the stress on the muscle during my pauses unless using to breathe in order to try to get an extra rep.
I am basing my training off of the book Beyond Brawn 2. I have read a lot of books but this one was the most no hype all common sense approach to training. He is very big on injury prevention and continuing to make progress well into the latter years or most lifters. I definitely recommend people have a look at this book. Everything I know to be true from my years of experience and self education has been addressed in the book. Definitely not gimmicky just get in and work hard, make sure you are progressing and take a short break when progress stops.