Answering (1) for myself, I do everything Meteor in Coffeescript, and in fact I'm playing around with the idea of maintaining a Coffee-fork of Telescope, as I'm integrating it into my app.

Regarding CS: I don't think the meteor community looks at it particularly differently to the JS community in general; some people use it, some don't.

It's supported by the framework; I've used it on a few projects but now I'm moving away from it (I find the hassles of communicating with non-CS users about bugs etc outweigh the benefits it gives me). That's totally a personal opinion though.

I'll let Tom answer your first question, but regarding the backend database so far only Mongo is supported, although more database options are coming (see the Meteor roadmap here: https://trello.com/board/meteor-roadmap/508721606e02bb9d5700... under "Later").