Yes, you are limited to 20 minutes at full HD. Primary function is a still camera, video is secondary. All the DSLR's have about the same time limits on video.

Make sure ACR is up to date, you might have to wait a bit for Adobe to release updates or you could covert to jpeg / tiff in View NX 2 and then open in CS5

Most modern Nikkor lenses include an internal computer module (CPU) that communicates with the camera to provide information such as focal length, focus position etc. When such lenses are used, the camera gets the information it needs to permit use of all exposure modes: (P) program, (S) shutter priority, (A) aperture priority, and (M) manual exposure control.

Older and some special lenses do not include the computer. These are “non-CPU” lenses. With these lenses, the camera can only function correctly in the (A) aperture priority and (M) manual modes. According to the specification you quote, this only works with the Spot Metering and Center-Weighted exposure metering modes. Some of the more complex “matrix metering” modes require a CPU lens.

Many Nikon cameras include a focus assist feature that uses the focusing sensor(s) to produce a visual indication in the viewfinder. This helps when manually focusing the lens. According to the quoted specification, the lens has to have an aperture of f/5.6 or larger (faster) in order for this feature to work correctly with the D800.

There are some exceptions for special lenses, for instance certain PC Nikkor lenses. A complete listing of lenses with their capabilities and compatibilities can be found on pages 371 to 374 of the “D800 User’s Manual.” The manual can be downloaded from the “support” section of this web site.

No, Nikon video is recorded on .mov files

I know of no software available to do that conversion.