Upgrading from D3000
Short version (I say this twice a week): Get a refurb D5100 or D5200, whichever's cheaper.
Agreed. Crawl, walk, jog, run. A d5100 or d5200 will be a welcomed treat, and it won't cost near as much as a d7100. Once you really know and understand photography, that will be a better time to jump up to an advanced DX body. Get some decent glass now though.