Good god no, never overwrite a raw file, its your backup so save as a separate file in a different folder. Your processing might look great today, but tomorrow you might think differently and cant go back once its overwritten.
For the majority of mine I save to a print output sized large jpeg, a medium sized jpeg, and two site specific sizes.
Large I save at 12 x 9 240-300dpi, medium is around 8 x 6 same dpi, for here its 800 pixels on the long axis and for ephotozine its 600 pixels on the long axis, the later two are usually saved at 72dpi.
All the resize procedures are saved as actions, so its just one click to resize to each of the formats.
Original un altered raws are saved in a folder marked raw file vault and then dated sub folders (this is my default import folder, dated folders are created automatically on import).
Jpegs are saved in a separate folder with sub folders sorted by subject, each of these folders then has sub folders sorted by output size.
Though it took a little while to sort out initially the bonus is that now I can wiz through processing and saving quite quickly and always know exactly where images are, and of course I have the original file just as it came out of the camera for back up/re working etc.