If you speak with a Family Law attorney, he/she would say the same thing I'm about to say - you can't just pick a separation date to suit either party's needs. If you separated in 2012, you separated in 2012. It is certainly possible that USCIS will consider the separation date when he applies for Naturalization and ask for proofs that the relationship was bona fide. He should work with an immigration attorney when the time comes.
That should be fine. Though the income for 2011 and 2012 will be listed, the focus is on the income for 2013. There is no "time limit" but keep in mind that you are out of status until the package is filed. It's best to work with an attorney - you don't want to end up back in removal proceedings!
If you move, you have to file a change of address form within 10 days, and that means your case could get transferred to the new location. If you're ok with that, go ahead. Perhaps discuss with counsel.