1) Absolutely no high intensity cardio (I've been too nauseated sick/lethargic since day 2 to even attempt it anyway). Your glycogen stores are way to low, you'll enter catabolic states. This diet is ROUGH, mentally and physically, I went paint balling on the 3rd day, and spend most of the night dry heaving from extreme nausea and headache. Just take it easy, walk 2-3 miles... even that makes me insanely dizzy anymore, if I ran I'd probably passout.
2) Yes, you should probably stick to 3-4 days of weights, as you'll need to up the calories on those days, but you won't want 6 days of 'upped carb/food intake'.
3) I dunno, I haven't personally followed a circuit training routine either... Probably should?
Best of luck, and I'd highly suggest a nice re-feed the day before you start, because you'll be missing food