Hi there!
You'll find Pocket eDGes (US, anyway) at Amazon, ebay and (if you want to watch for it to come up again) Woot.com. Check
www.entourageedge.com for their list of sellers in other countries.
You can leave it on 1.6 (Dingo) without missing much, or you can take a small risk and update to 2.2 (Ermine) which is very nice but not officially supported. It seems a lot of new buyers are rooting the device, but that's because they like messing around with gadgets, as far as I can tell!

It certainly isn't necessary to root it.
I'm not sure exactly what you mean about how you want to use it for your writing. It works fine with most keyboards, and you can edit on the e-ink side if you convert your work to epub or pdf, so I would imagine you can do what you want. It has Docs to Go on it, too, on the LCD side.
I think it would be a very handy tool for a writer. It's one of the uses I had in mind for mine (haven't done it yet -- too lazy

), especially being able to look up references as I need them without having to have 2 devices, or taking notes (journals) on the e-ink side while I research.
The only thing I wonder about is whether you would be happier with a full-sized edge (an EE) if you can find one. The 9.7" screen would be much nicer for marking up your manuscripts, and the 10.1" LCD would be nice, too. It's a bit heavy, but if you are at a desk or using a bookstand that won't matter.
Good luck!
Oh, and check out the forum at
http://www.entourageedge.com/forums/forum.php if you haven't already!