Don't worry about the air law exam-I read the Jeremy Pratt air law section(not the comms)and passed without any problems.
I would recommend you get the PPL Confuser book as it tests the knowledge you have read. It's very easy to just read something and not properly absorb it-especially with something incredibly dull(although vital) like air law. The Confuser is just like the exams themselves and is great preparation.
Good luck!
