1. There was
a similar thread here on PSG just a few days ago. Scroll down to my 1st posting in that thread.
2. Only color problems were discussed in that thread. However, you also mentioned that your images were "more grainy". That's a separate problem. In fact, it's not actually grain you are seeing, but compression artifacts from the forum uploader software. To save space and reduce the time it takes to display a forum page, they have it set to produce highly compressed versions of images that you upload.
In other forums, if you down-rez your images to a small size and compress them yourselves, the forum software won't modify your image -- it will just pass it along unmodified. If that's the case here, I haven't found the magic conditions for it to happen, so I just live with it and urge viewers to click on the thumbnail to see the actual image.
3. The link you posted is certainly on the right track by suggesting that you only post in sRGB, however, should you want to continue to do most of your post-processing in, say, ProPhoto or Adobe RGB, you can convert to sRGB as the next to last step before saving a copy as a JPG. Instead of their suggestion to manually change the working color space and then manually add some saturation, use the Edit / "Convert to profile..." command and set the target color space to sRGB.
HTH,
Tom M