Identity column in columnstore index
Identity columns are not truly compressed in Columnstore Indexes in SQL Server 2012 or in SQL Server 2014. It will all truly depend on the workload that you are experiencing. If your workload will include the identity column, then you can very beautifully take advantage of Segment elimination.

From the compression point of view - Columnstore will provide you with better compression than page typically does. Typically. Please test it before advancing to production. 

Your biggest problem in SQL Server 2012 will be a very weak implementation of the Batch Mode, and there is nothing you can do about it.