1) The resolution setting matters only for printing, not web display (and not even for straight photo printing since the printer driver takes care of it...so really, it matters only for page layout prior to printing).
2) Bicubic Sharper, and often that's not sharp enough for a substantial reduction, so a little unsharp mask helps.
3) A 1200x800ish image isn't very large, so 100 is fine. 70 wouldn't likely be noticeable, but you don't want to re-compress much (I output at 95% during RAW conversion, then keep quality at max for the rest of the workflow, unless I'm uploading to a site with small file size restrictions). Lower quality was useful before broadband was the norm.
4) Optimized. Progressive saves a 'layered' image, so when downloaded you see a low res image that 'cleans up'. Again, useful before broadband.
5) sRGB is the default color space for web browsers, so you see your output as everyone sees it. You should also embed the ICC profile, as many browsers are color-managed (i.e. respect the embedded ICC profile) so what you see is truly what others get. But for example, Chrome under Win7 is apparently not color-managed; all browsers under Mac OS X are color-managed.
Here's a test - if the race car is yellow, your browser is color-managed, but if it's purple, the embedded ICC profile is being ignored (it's yellow in Safari on my Mac, but purple in Safari on my iPhone running iOS 6).