1. I don't think that I pay an HD technology fee. It may have been one of the fees that I had to fight about getting removed, but I don't think so. I actually think it is one of those fees that the rep on the phone tried to convince me I needed to pay, but I did not. If I recall correctly, it is what you have to pay for renting their HD equipment, versus an SD DVR, etc.
2. I've never heard of a negative result from removing a CableCARD. You just lose the channels that you need it for.
3. Correct. Comcast charges nothing for the Mini. They are not part of that equation. As I've seen someone else describe it, they don't even know that you have it. From my perspective, that is a big deal. I was tired of paying Comcast for a second CableCARD and digital outlet fee on top of the Tivo fees. I went with a lifetime service on my Mini, so it is free to use as long as it lasts.