When I was younger, I was a pretty athletic guy who got into weight training (and spent time on T-Nation) and was in generally good shape till I turned 22. Then, for some reason, I slowly lost all motivation to take care of myself and, over a 3 year period, went from 200lb with low body fat, lots of muscle and stamina, and good diet (based off of Berardi's Precision Nutrition) to 300lb with a ton of fat, some muscle left, very little stamina, and a horrible diet of eating whatever the fuck I want, whenever the fuck I want.
Whereas before I was very active with lots of sports, weightlifting, etc., I've become completely sedentary to the point where over a 24 hour period I probably spent less than an hour of it off a chair or bed. Walking for ten minutes left me aching, sweating, and slightly out of breath.
Thankfully I've gotten myself out of this funk and am ready to get back into shape. My first step was fixing my diet (again using PN as my guide) and I'm aware that the vast majority of my improvement will come from this change. However, I also want to be physically fit again. I've started some very rudimentary activity (30-40min min walking on twice a day) so that I don't shock my system when I'm ready to start weight lifting again. My question is how I should approach the weight lifting.
I know that with someone who's obese and has had almost no muscle development over the course of his/her life, you should start extremely lightly. But the examples I've heard of usually describe someone who can barely do pushups and bodyweight squats. As someone who was previously active, I can still do pushups, bench, deadlift and squat with a couple of plates albeit feeling very uncomfortable later. Should I jump back into my old weight lifting routines except with lighter weights? Or is there special attention I need to provide to parts of my body, such as my joints, hamstrings, etc, that have seen very little strenuous activity over the past few years?