I agree as well with the two other posts. YOu shouldn't do the P&B with the MC. Just do it by itself. When i did the MC, i couldn't stomach the SWF, so i did just take Smooth MOve tea, or whatever lax. tea you can find. I drank it before bed and in the morning to keep things moving.
As far as the 30 day juice fast, I'd say you certainly can then do the P&B with that. I'd recommend some enemas/colonics while you're doing that too, it should be the mother of all Bowel Cleanses if you stick to it for a month.
I would recommend sitting down and just reading through the Master Cleanse Forum , and the Bowel Cleanse Forum for an hour or so, you should get all your answers there. Also look at the FAQ's at the top of the forum's page, there's lots of good information in there.
I'm on a Bowel Cleanse right now myself, and i'm on here every day looking for more tips and pointers. Good luck with everything, you can do it!!