I can answer ONE of those questions.
A 2k scan provides 2000 pixels horizontally. 1080p is 1920 pixels wide, so yeah, a 2k scan is pretty much 1080p.
Now if the 16mm reduction has 2k worth of information is another question all to itself that I cannot answer.
If no one knows, the best way to go is to take some frames and compare a 720p resize to the source and see if there is any less detail.
If it's there, it would be worth preserving.