I'd like to address your a, b, c points directly.
a) when communities will launch (or shortly afterwards) there will be more types of communities available, including one where only members can post or one where only members can post or comment. This is important: There won't be a possibility to change the type of the community, at least not in the first iterations of Hive communities (meaning you can't switch between allowing guest posting and not allowing guest posting in your community, once you created your community and once you chose its type). More about this here.
b) this is high on the list of priorities of roadscape to solve ('cross-posting' and / or resteeming to other communities), but won't be available at launch
c) the hive id has a reason - so that there can't be two identical communities, even if they are named identically. On an interface that understands Hive communities, you won't see the hive id as a tag, you will see the name of the community. Check any community on the beta interface as opposed to the steemit.com or steempeak.com interfaces and you will see the difference. Once Hive communities will be supported on the main interfaces, that won't be an issue.

Steem-Engine "beta" is available here:
https://next.steem-engine.com

But they still need to work on it.