But my question is, how many books do I need to buy?
I hear the book comes in 2 seperate volumes. And that there are also workbooks and a "teachers handbook". Also there is a UK and a USA version of the books.

If I am working by myself then clearly I will need an exercise answer key. Does the regular Athenaze not contain an answer key? If that is the case then it is a little annoying that I would need to fork out $100 for the teachers edition (amazon price).
What about the "workbook"? Is this strictly neccesary or just supplemental?
What is the difference between the US and UK versions?
Also, based on my ability, should I start with Volume I or move straight into volume 2? I have already done some Koine, I know the 3 declensions, present, middle passive, aorist and future verb conjugations and probably know most of the vocab that appears more than 50 times in the Bible. But I have no Attic. I am thinking that Volume 1 may be a waste of time and money based on what I already know, but then again Volume 2 may be throwing myself in the deep end if I haven't learnt all the vocab from volume 1.