My PP for B&W is like this, open image, adjust levels, desaturate, adjust brightness/contrast, maybe burn or dodge, clone or heal in this process too.. save with another file as to protect the original. Thats about it..
Sometimes depending on the type of exposure the adjustments might only be needed in part of a photo, in this case I use the adjustment layer tool - which is the little yin/yang symbol on the bottom of the layers palete.
Once you have made whatever adjustment to the image via that individual adjustment layer you can remove the effects individually by painting back over that layer with the brush tool and in black..
By adjusting the opacity of the brush, you can control how much of the previous adjustment you may want to remove.
You might want to do this say for a photo that has part under exposure and part over exposure: for instance if you wanted to bring up the mid tones in the under exposured part, I would control that with an adjustment layer of levels, then increase the midtones.. Noticably the hightlights would begin to get brighter and if I wanted to tone them down I would paint over those bits.
Once completed you can make say three files, the original - that has not been touched, the flattened image ie; jpg etc and the layered
PS file for future work, so you can go back and work it more down the track?
Hope this process may help you and others
Regards
Sean
PS I use this same process for colour work, just dont desaturate image. - you proberly knew that but someone may get confused -ciao