What is the Europe release date? I'd like to know whether it's worth forking out on the international postage cost, or waiting for the game to be released in Europe.
I don't think there's an exact date, but I think it was said early summer?
How large is the downloaded version? I don't have internet access at home, and can't download too much using my friends connection.
It's less than 1gb, I think closer to 900mb actually.
Is it possible/allowed to write the downloaded version to a disk?
Yes, you can and are certainly allowed to create a backup and burn it onto a DVD. However there's also no limit to how many times you can redownload as well.
Does the downloaded version require an internet connection to do anything other than the actual downloading process? - Does the packaged version require an internet connection to play?
It does not require an internet connection to play or install. You will need an internet connection to authenticate your serial # (though this is done automatically when you purchase through Stardock's online store, even if it's the box version if I recall correctly). With a non-Stardock boxed version, such as if you were to wait for Kalypso to distribute, you would be able to play out of the box without authenticating your key, however you would need to do that once (per Windows install) to download updates.
Hope this helps! Any more questions, feel free to ask!