question #1-- AGVT is for mass gaining, period. Body Comp is for fat loss.
question #2-- each bodypart has two exercise schemes and three set/rep schemes. If you want to think of it this way, you do sessions "A" and "B" for each bodypart with 10x5. Then do sessions "A" and "B" with 10x4. Then do sessions "A" and "B" with 10x3.
question #3-- yes, a 10-pound dbell would be correct.
question #4-- don't get too anal about teh angle. Adjust the bench about one-third of the way up from flat. That's about 30 degrees.
Question #5-- curiously, I have read quite a few times (and have experienced it myself) that overhead pressing doesn't do very well with GVT. Stick with the bench pressing variants.
I have a feeling that I've done more harm than good with my answer to question 2. But I hope I've given you some good answers.