Is there any idea of using yellow, orange or red filters when shooting for BW?
You do all that doing post processing of the color raw file?
What if the camera has been BW modified?
To answer the last question: if the camera is modified to be monochrome, it pays to process the RAW in a special converter. For example, Monochrome2DNG, which is the one I use for my NEX-5N Monochrome camera.
Using some kind of filtration to cut down on blue etc. has a long-standing history for film-based b/w. If the camera is not true monochrome, I would not use a filter as this effectively would lower the attainable resolution. Instead, emulate the effect later in post-processing. For a monochrome camera, it makes sense to use a filter to reduce brightness of sky or selectively bring out skin rendition. I often use a deep yellow, orange, or red filter on my NEX-5N, if not going the whole way into IR with an IR-filter.