PRETTY LITTLE LIARS: who is 'A'? (TV series)?

I really want to know who 'A' is... and I know I'll be spoiling the
ending for myself and whatnot, but alright here is what I know so far
based on what I read people wrote is from the book...

@@@@@@@@@@@ SPOILER ALERT@@@@@@@@

Alright, so I know that Alison had a crazy twin sister Courtney who
stole Alison's identity because well... she was crazy! I also know
that Alison killed Courtney as revenge because Alison was accidentally
taken to the hospital instead of Courtney (who is pretending to be
Alison). I also know (I hope I got this right) that the real Alison
wasn't friends with Spencer, Aria, Emily, and Hannah, but the fake
Alison AKA Courtney was, so the real Alison is 'A' and is messing with
Spencer, Aria, Emily, and Hannah?
I also read that Mona was 'A' in the beginning (before the real
Alison) because she found Alison's diary. She also ran Hannah over
(which already happened in the TV series) and then somebody killed
Mona??? That didn't happen in the TV series...

SO, my questions are:
Who is 'A' at this point in the TV series?
Where is the real Alison?
Who killed Ian?
and
is the TV series going by the book?

Thank you!!!!