I don't do a lot with pdfs, so can't answer most of your questions. Here is a link to the User Guide and videos that should tell you what you want to know:
http://entourageedge.com/support/
Calibre works fine with the eDGe. Books can be loaded through USB cable connection with a PC, wirelessly from email or Dropbox or over your LAN, or direct from the internet.
Compared to the Onyx Boox M9 series the eDGe is heavier (3 lbs) and does not have the Pearl e-ink screen.
Wireless performance is very good, IMHO. Internet browsing is also very good, although my big eDGe has the browser-crashing issue that some have. Annoying, but I keep getting back on that horse!
If you stick with the earlier OS (Dingo, Android 1.6) you can probably avoid the browser crashes.
The writing works fine for me, but I don't know whether it would please you. It's too bad you can't try it somewhere.
P.S. You do know, I hope, that the eDGe does not have access to the Google Market (unless you root it, etc.), which makes finding all the apps you might want more challenging.
