I've got two questions.

I've got arthritis (though it's being handled fairly well with some good meds), so is there anything I should be more careful of or avoid? I'm very careful with knee stuff and making sure I've got the proper form for knee moves.
I'd also like to reiterate the question about having large amounts of weight to lose. I still need to lose 50-80 lbs. Should I just do the workout and diet as prescribed and work harder and longer, or is there something else I should do as well?
Thanks! The book is terrific! I'm going to start rereading it again this weekend.