Tom:
actually everything you asked does make a difference and are individual to each person. i believe they are all coverd in the book and article links but feel free to always ask questions.
as to when: usually after the rest of all your other work for if you are training correctly you are activating your TVA and subsequently the rest of the core on every rep, so if you do your core/abs 1st. you are tiring out the muscles that stabilize your spine & protect you from injury - all movement begins from the deep core and the TVA fires 30 -50 millisec. before any limbs move to stabilize & protect the spine and coordinate the bodies movment while transfering power (in those who have a properly functioning core)
If you have a weakness, injury or are only doing core work then you can do it at the start of your workout but do not follow it with heavy strength or power exercises or you can cause an injury.
Too much? - you reps should be less then 15 with extra resistance unless you are training for injury rehab, spinal stabilization, postural endurance or sports endurance. The rectus & obliques are composed of type II strength fibers and function to protect against impact, spinal hyperextension and perform explosive rotation.
Daily core/ ab work can be done as long as your train different muscles & movements to prevent overtraining.
The book is good, please realize a lot has been added since it was printed but the principles & ideas are still the same - just other exercises are used;
primarily the physioball. Just replace the floor crunch with a proper physioball crunch and you will be fine!
If you really want in depth info on all the muscles, testing, program design and beginner - advanced exercises the best thing is the CHEK Institutes core conditioning pack of 5 videos & manuals (its where I got most of this info!)
http://www.chekinstitute.com/products_specific.cfm?product=45&corr=yes
S
SORRY FOR THE DOUBLE POST - I WENT TO EDIT & ADD THE LINK BUT IT DOUBLE POSTED