Upload & Sell: On
Dan - Whatever color space you choose to edit your images in Ps is your decision. Arguments can be made for sRGB, AdobeRGB or even ProPhoto RGB, but you need to understand why and when to use different spaces. Whatever you use, you should convert images that are going to be displayed on the web to sRGB if they aren't already in that space - and embed that profile in the image so profile aware browsers and use the profile to help display properly.
For scanning color negs, there really is no such thing as a "raw" scan, untouched by the scanning software. Well, I can force my drum scanning software to do that, but the results are really really ugly and would be completely uncorrectable in Photoshop. You actually have to let the scanning app do its job, but coax it in the right direction.
I don't know how you check the number in your various scanning apps, but there is usually some sort of probe that will give you before and after RGB pixel values and also controls that let you alter the default settings for black point and white point target points. In Photoshop, you just have to have your Info Palette open and move your cursor over the area you want to monitor. The Info Palette will tell you the numbers, in RGB, Lab, CMYK, Grayscale, Total Ink, Actual Color, among others. You can set the readout to what you want, but either RGB or Actual Color is preferred most of the time. You can also place sticky probes (up to four of them) in the image in Ps to continually monitor up to four specific areas while you are doing color and tonal corrections. There are a couple of ways to place those probe points, but the easiest is to Shift-Click while you have your Curves (or whatever) dialog open. The Info Palette is perhaps the most important palette to keep open and monitored while working on images.