It is not asking for an IMEI, where did you get that?

Why a country and an operator? Google Play offers content based on that (some content may be available for download in one country and for one operator, while unavailable for others) - you can choose whichever you want, though - it doesn't have to be your country and operator.

EDIT:
Version 0.3.1 with some more fixes pushed to Github & OpenRepos.

It logs in to https://google.com/accounts/ClientLogin and then uses the Market API. I was thinking about implementing standard OAuth authentication, but that would require an app key, which would be very likely to be revoked by Google, causing often app breakage.

I believe this will indeed count as a device at Google (as you are first generating your Device ID) and should act as Galaxy Nexus, if you are using the recommended method.