1) hard to say. i started 2 month ago, and maybe spend about 3 hours a day on average on app-related stuff. when i started i only had little experience in rails, but had absolutly no experience in backbone. so it took me quite a while to get into it.

2) to start out i read this http://coenraets.org/blog/2011/12/backbone-js-wine-cellar-tu... and then everytime i was stuck i search for a solution on stackoverflow. i'm not using nodejs btw. just backbone for the frontend. once you done a couple of tutorials, i recommend using http://www.brunch.io

3) the themes are coming from my rails backend. i have a mongodb database on http://www.mongolab.com. the backbone app makes a request to my rails server and gets a respond as json. you can see how that looks like at http://www.themescroller.com/themes.json