On the first part the D7000 has AF fine tune - though I find Nikon's advice accurate - it is rarely needed. Most fine tune issues are "user misunderstanding" in that they only occur using AF targets where the risk of AF system mis focus is high. I have not done full video test yet but if video works the same as on the D3/300 s 1/ In LiveView hand held mode changing the aperture whilst recoding results in the camera correcting the exposure during recording. Ideally you need to be working from a tripod to avoid camera movement when changing the aperture. 2/ in LiveView tripod mode the aperture can be changed but the exposure remains constant. You can start recording with part of the image underexposed and change exposure to get detail in the shadow area. Ideally what is in shadow needs to be interesting enough for the viewer not to notice part of the image becoming over exposed.
Photography is a bit like archery. A technically better camera, lens or arrow may not hit the target as often as it could if the photographer or archer does not practice enough.