1. Agree with both HelenD and tacpot - do them in advance if you're doing an intensive course, otherwise mix them in with the flying. All I'd add is the fairly obvious point that if you're doing them while you fly then don't get behind with the exams - I know several people who have had parts of their training held up because they hadn't got the exams done (my club required Air Law before first solo and Nav and Met before the Navexs). The most extreme example was one bloke who had 5 exams to do in the 3 days before his skills test
2 & 3 - agree again. Searching for 'Thom', 'Pratt' and 'headset' in this forum will find many views
As for 4., there are adverts in Pilot and Flyer, but do you really need groundschool? The PPL exams aren't hard, and if your instructor isn't prepared to help you with the bits you find difficult then you are at the wrong school! Read the books, buy a copy of the
PPL Confuser (it's in the Transair catalogue) and work through the questions in that. You'll pass the exams no problem
(edit: I don't disagree with cloud69 either, but that post wasn't there when I started typing
)