I'm a moderator at Nikonians.org and a more detailed discussion to help you could be handled more effectively there.
Generally speaking the D7000 is set up with defaults for a consumer orientation. That means images are a little softer and brighter to be optimized for small prints shared among friends or on the web. When you look at magnified images optimized for small prints, it will look soft. The assumption is if you are more advanced, you'll also know or learn to optimize your settings. Frustratiing but true. :)
For me, that means increasing the in camera sharpening, keeping noise reduction off for most situations, and using a single focus point rather than letting the camera automatically select the focus point. If you choose a single focus point, you have to watch how you use it. You need to place the point on the part of your subject that needs the sharpest focus. Maybe it is the eye of a person, or for landscapes about 1/3 of the way into the frame.
Also keep in mind that a 16 MB image is going to show more resolution and reveal technique errors that were not seen on 12 MB images. We saw the same thing when we moved to the D200 from D100/D70 cameras.
Generally the camera and lenses are pretty good. You can buy better lenses, but it's best to learn to optimize the gear you have. Make sure you have enough light to freeze the subject and eliminate movement. Your shutter speeds need to be fast enough to hand hold - 1/500 sec or more is best if you are testing. Don't shoot at the extremes of your zoom and expect perfection - most lenses perform better if you stay away from maximum and minimum focal lengths. Stop down your aperture a little to f/6.3 or even f/8. Most lenses perform better stopped down a stop or two - which also gives you more depth of field. And for testing, pick a simple target with clear contrasting edges. It normally takes a little practice. You have to make your errors predictable - not just your successes. Know when you are at or beyond your limits.
Hope this helps.
The Canon 5D Mark III is a full frame sensor vs the crop sensor in the Nikon D7000. Also about $2300 between the two bodies. Really depends on your budget and what you want to do. If you are asking this question you most likely don't need to spend the money on the 5D.
The boxes aren't sealed that I know of. If you are worried about it you can take a picture, press the play button to see the picture and if the title is the number "1" then you've taken the first picture.
The weight is greater because of the manuals and accessories included. There are two 300+ page manuals (one in English, one Spanish) which alone weigh 1.5 lbs. Add in the weight of the battery charger, battery, neck strap, USB and audio cables, software, body cap, etc and the weight quickly adds up. I ordered the body only D7000. The UPS label shows 6 pounds. When I put the D7000 package (without the shipping box and packing) on the scale, it was a little over 5 lbs. I'm sure the ones that come with a lens would have a 7 pound shipping weight.
I bought the D7000 in Nov 2014 and yes, it did come in the gold Nikon box and it did have the warranty card with it. It came from Nikon. Was not a gray market camera, but the real one. I love this camera body a lot and am glad I did upgrade from the D90!