I'll number it out for you:
1.) Yes, if you use the 2.0 file linked here, it will take you there. But why do you want to go to 2.1?
2.) Me too, once. But I found that even then it might not have been needed.
3.) You could use this thread to downgrade to 2.0 and then do the 2.0.1 manual install with root
4.) Here's a few other idea's:
Root Droid 1 - regardless of OS version
Root the A855 without RSD Lite + make it ROM ready