There are plenty of Raw converters available for free or very cheap, this is a very good one (leave a $5 or 10 donation to the site)
http://www.rawtherapee.com/ even has it's own browser that is kept up to date and can open virtually any Raw file.
If you open a Jpeg then manipulate the image any data not required by the manipulation will be 'dumped' and if you save as the original file name the image will deteriorate. When working with Jpeg use the original file as a 'Master' ALWAYS rename if any manipulation has been done. Just add an 'a' to the file name, anything will do as long as it's different.
The beauty of Raw files is they NEVER get written to, any corrections you make are written to a 'sidecar' file (xmp) which is like a filter through which the data is reproduced for the screen, they don't even have colour space until you define it by opening it up in Photoshop or similar, that information is held in the 'sidecar' file too.
I always save as Tiff for my final image and Psd for a 'work in progress', both of which are lossless, and I always save as 16bit.
A B&W file from the camera IS just a desaturated image usually to the Red channel.
Here is a B&W conversion method which works with most versions of Photoshop;-
Open your colour image
Open 2 Hue/Saturation Adjustment Layers.
Rename the top one 'Film' and desaturate (slide the Saturation control all the way to the left)
Rename the middle Layer 'Filter' and set the blend mode to color.
By altering the Hue slider on the 'Filter' layer you can select any channel and even in between channels to get the conversion you want.
By using the Lasso Tool selecting say the sky and feathering lots then calling up a Levels Adjustment Layer, you can alter the tones just in the sky, or the middle distance, or the foreground, whatever is selected, the Adjustment Layer will provide the mask. Don't forget to feather lots. Works best on 16 bit files as this technique really pulls a file to pieces and 16bit will maintain smooth gradations in the tones.
Chris