This is kind of a multipart question.

I am contemplating getting a polarizing filter for use with my 4x5 setup. I shoot only black and white. Is it likely that a polarizing filter would become an important part of my photography, when shooting black and white? I know that many use it for color saturation in color photography. Also, I have read that the filter gives me aprox. 2 stop less light. When applying this to a moderately slow lens, I am assuming that viewing the image on the ground glass will be difficult. However, isn't it important that I see a pretty clear image on my ground glass to determine the proper adjustment of the filter, to properly polarize the light? Lastly, is it safe to critically focus on the ground glass before applying the filter to the lens?

Thanks!!