A few answers: I shoot lots of chromakey stuff with the Varicam, recording in the camera. The post guys I work with are always able to pull a great key with the DVCPRO HD compression. Obviously appropriate lighting is essential, but that goes for all formats.
Yes, you can use the 1200 to capture on set to a Powerbook.
Now, as far as question 3-you definitely should use a DP who’s familiar with the camera, or at least have someone on set who knows it well. You’d be wasting your money otherwise. The SDX900 has a built-in setup that’s pretty decent as a starting point, but the Varicam doesn’t. I’ve rented bodies before that are set up really bad and had I used them straight from the shop, I would have been in trouble. Also, if you don’t have someone around who fully understands what the camera is capable of, you may really be missing out. I highly recommend a tech, or a DP with some great looking setups and a command of the camera.
I hope this helps!
Chris B.