I cant answer all of your questions. But I will make a few comments.

1. Annotating on the eDGe is very natural and works well.
2. There is a slight lag to handwriting, but easy to get used to.
3. Using the eDGe for annotating is definitely worthwhile in my opinion. It is much better than paper in my opinion, and very productive.

I have been using the eDGe to read PDF files that I create with Adobe Acrobat Pro. The eDGe faithfully shows all annotations, and can handle web links etc that I create with Acrobat. I have no idea about going the other way, i.e. taking an eDGe annotated PDF and reading it on a PC. Interestingly, the software in the iPad for reading PDF files will NOT show any annotations made with Acrobat Pro.

I hope this is helpful.