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Yes, it requires to use very fast HDDs until you finish transcoding to some non-raw format. Comparable RED raw files are from 3x to 5x smaller. Other good format for raw storage is Cineform raw, it is also much smaller and much less demanding to disk infrastructure.
Yep, you can do it. Go to http://cineform.com/, check their blog and downloads. They have conversion utility that can work with individual DNG files (Black Magic produces individual frame files). Resulting format is Cineform raw, and you can define compression ratio used. It is called DPX2CF.exe, also comes with Cineform Studio Premium.
You can also try Blackmagic Cinema Camera Cineform GUI Utility
Most probably yes. You can use either internal (with PCI-E cards) or external solutions (using USB 3.0 or Thunderbolt).
Thunderbolt based solutions
USB 3.0 solutions are usually much more affordable and you can find more options.
If you are actively shooting they will be much better approach, as you could leave drives inside bay and store it so, or just remove drives and put them into storage.
Both ways will be much cheaper than very rare Thunderbolt.
USB 3.0 based solutions
According to Adobe representatives you must not expect smooth working, as CinemaDNG support is not in production state yet.
Most probably you'll be required to have intermediate step to reencode it into Cineform RAW or any of debayered formats for smoother work.
See Cineform question above.
Answer here is quite simple. Sensor of the camera has bayer structure, it is looking like this:
And 4:4:4 format require full color information for each pixel. In top cinema cameras this is done combining 4 sensor values (2xG, B, R), and requires 4x of sensor resolution.
As you know, resolution of Black Magic camera is too low, so you can't make true 4:4:4 debayered format. Hence they use 4:2:2 variations.