D5100 and D7000 are fine cameras, and the IQ is virtually the same. I currently use a D200, D300, D5100. I bought the D5100 for several reasons. I was waiting for the D300 replacement to be announced and wanted the articulating screen for shooting over my head in museums, and from near ground level with wide angle lenses, and it works well for these purposes. Given enough time to setup it performs admirably through the view finder but the miss rate is high on fast moving subjects. IF I was only buying one APS-C camera today it would be the D7000, even if I was a casual user because of the far better access to controls on the D7000.
The D7000 is weather proof, has a much tougher body, much more sophisticated focus and tracking system for fast moving subjects, better view finder, MUCH better camera controls that are far easier and faster to manipulate than the D5100 even if using your camera infrequently.
The D5100 to me is harder to use, and takes extra time between shots even when you know exactly what you want. It takes great pictures with my best old manual focus lenses, like my Nikon 85mm f/1.4 ED. But give up the metering and also auto-focus on some of my older lenses. If you have been doing this for 50+ years metering by sight is okay, but getting to the controls to fine tune the settings and watching a shot disappear while setting the controls drives me a little nuts. I want to be looking at the subject and thinking, not using my eyes to press buttons not watching some blinking LEDs. If you are shooting the new aps-c lenses and shoot ttl flash instead of the more reliable manual flash then this ceases to be a serious issue on stationary subjects. Real life moves fast and the D5100 is not fast but has a very high IQ.
Whether you buy the D5100 or the D7000 be sure your firmware is updated before you use it. Nikon had a serious problem with memory cards being recognized, or if recognized initially would frequently stop recognizing the cards during a shoot. It required pulling the memory card out and pushing it in again. The new firmware solves this issue.
On the lens, if I had one lens only and wanted to hold down on the price. I would check to see if B&H http://www.bhphotovideo.com/c/product/581247-REG/Tamron_AFB003NII_700_18_270mm_f_3_5_6_3_Di_II_VC.html still has the Tamron closing out for 400 bucks The zoom binding is a genuine issue, but the lens is sharp as a tack from 18-270mm with good contrast. The difference between 270mm and 300mm is negligible, while the advantage of having 18mm instead of 28mm is huge when taking picture. This lens is a great value at the close out price.
