Distance learning
Hi Rob, just from my own experience of distance learning with BGS a few years ago, took me about a year to complete the course and pass the exams, and that was with about 3 hours a night study average (ok, sometimes less when I really wasn't up for it) and usually at least one fairly busy study day at the weekend, whilst working a 9 to 5 job.
But if you disciplined in your approach to the study, and set regular goals for your progress (in fact BGS kinda did that for you), then Id say a year or so is probably about right, whilst working full time. I'm sure it could be done a tad quicker, but that suited me.
As for any advanced reading, if it was me, I wouldnt necessarily try and race ahead with ATPL stuff, simply because without being on a course and having a timeline and structure to it, it could appear a bit daunting...however I would really read things like the PPL Thom books again and get a very thorough understanding of subjects like met, nav, if you have a very good PPL level grasp of these things, it really does help at ATPL.
Good luck.