Love that you are documenting this as you go. Why Couchbase vs MongoDB or ...? What will you use for the front end? Ember? Angular?
John is doing the database work. I'll have to let him answer the question about Couchbase. As for Ember or Angular, we'll decide that next week when we work on the results page. We don't have much experience with either of them. Do you have a recommendation?
FYI MongoDB also has auto-sharding. Not that I've ever used it... But I have used Couch. The views and shows in Couch ARE really nice; they let you format your data before it ever leaves the database, giving you a nice consistent API on top of your loosely structured data. I've thought about moving from CouchDB to Mongo but I'd really miss that often-overlooked feature.
I don't have any experience with either Angular or Ember, but I will be trying to learn them this Fall. A friend says there is a huge Angular community in SLC, so if you want to hire additional help, that could be a motivation. I personally prefer Ember just from the reading and watching videos I've done. Their approach uses templating syntax that is very similar to Jinja (curly braces to embed code in HTML), whereas Angular adds tags straight into the DOM.