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If you have the cash the 55mm 2.8 is still one of the best lenses Nikon ever made. Even in manual mode combined with the 1.4x its a great lens. You will have to come up with lenses that are every day carry-around, so go with the kit and if you can afford it, go for your friends lenses.
You will have to use them in full manual, if they are not Nikons, don't bother. As for the flash, it might damage the body if you try to use it (check Nikon support). Also the 7100 won't do any of the ttl flash functions, you would be better off using the built-in flash. I think you should consider the 55-300/4.5-5.6 DX VR. Its less than $400 at B&H if you buy it alone. There is a Nikon kit with a wide angle and this lens included.
Unless you have more money than you need, stick with Canon. To replace your 2.8 glass won't be cheap. However if your lenses won't work on the new body and you have to buy new ones, the d7100 is a good camera.
My D800e has the same battery. I've shot ski scenes at -15F with no problems. Nikon is just being cautious.
I have been shooting a D800e for almost a year and have never had an image problem that I didn't cause myself. You mention that your having WB problems, this sounds like you are shooting JPEGs. If so try using the 2nd memory slot and shoot in NEF JPEG mode. Compare what you get, you might have some of those VERY obscure settings wrong.
Great sharp lens. The lens that I used most for portraits back in film days was the 105mm. That is the same as 70mm with a DX sensor. Many shooters like to gat back a bit and use a 135, but be careful if you use too long a focal length, you will get flat faces.
got all 13. I think the UHHs as a group are more inclined to be techie, and would see this test as easy. Most people really don't care about this stuff. If I took a quiz about movie stars I'd be off the left side of the chart!
You might not have a buffer problem. Sometimes when you take a burst of photos in low light or there is low contrast, the camera is trying to focus. If your shutter release is set so that the camera has to be in focus, it will lock up or take a long time between shots. Think about the photos you were trying to take and if they meet these conditions change the release setting. The actual focus won't change between shots.
CHOLLY makes the mistake of seeing a cropped image as the same as seeing a zoomed image. The only difference between a DX photo and an FF is the area of coverage. Noise (when your shooting in the dark) is the big difference.
Don't be put off by the snide remarks. The basic difference is the FF sensor is the same size as 35mm film. The APS-C is much smaller. Camera makers wanted their users to keep their lenses, so the sensors are in the same place on the different cameras. The FF lenses have to cover a larger sensor and because of the optics involved are really expensive. They came up with lenses that cover a smaller area and are only 30-50% the price of FF lenses. The catch is that if you buy a lens for the small sensor, you will get a picture that looks like a silent film on an FF camera. This topic could go on forever, but I hope you get the basic idea.