Re: Cable between TV and Receiver (when using multiple sources)?
I don't care for pull down video screens, so I would not do dual display unless you can arrange it so that a pull-down screen is not used. I would also put a bit more money into the front projector and not have the plasma. If this becomes your decision, plan on saving a bit of that plasma money to buy a new bulb in the future, especially if you plan to watch TV 10+ hours a day on it.
If you do go dual screen, and your receiver has only one HDMI out, you may want to consider either an HDMI Y-Cable, or a simple HDMI switch. You definitely want to use HDMI for both displays as it is the connection that will give the best possible picture.