I don't see why you couldn't use them, just not at the same time (and you won't be following "The Regimen"). Use BP in the morning and Retin-A at night. As for the moisturizer, do you want to use them both? You can of course alternate or combine them, but I don't know why you'd want to use two if one does the job.

I strongly advise you not to incorporate other things if you are just starting out the regimen. When your skin settles and gets used to the BP and has cleared then you can start incorporating one thing at the time and see if it works well with the regimen.

Thanks a lot for the answers