You won't need Vol 5 of Trevor Thom; that's more for commercial licences and the radio nav required for PPL will be covered in Vol 3. I did helicopter so didn't get Vol.1 but, even so, I'm not convinced of its worth. Perhaps other can comment but I would have thought the school would have provided the "how to fly it" and exercise and lesson plans. Vol 7 (Comms) can be replaced with CAP413 downloadable off the internet so that leaves Vol 2 (air Law & Met), Vol 3 (Gen Nav) Vol 4 (something to do with fixed wings things!), Vol 6 Human Factors!
Cheers
Whirls