Alfred,
Walter answered the “Yes” part for you. I’m not sure yet how much you can squeeze on there. It’s going to depend on the amount of compression you use. Compressor currently has 3 presets for encoding for HD DVD – 2 of them are H.264 based, while the other is MPEG-2 based, they are all at different bitrates.
I created a HD DVD a couple weeks ago to try it out. I just used a minute of footage, but everything worked great. I made one disc for 1080, and one for 720. Both ended up looking great on the 52″ Samsung 1080p LCD we were testing them on. I will tell you not to bother using the H.264, 6.75 Mbps encoder though – it was junk. I’m planning to do more tests soon using a dual layer DVD-R disc, which should allow you to get more content, but I’m not positive if the HD DVD players will support it yet – hence the reason I’m testing.
As for your question about having a control port for syncing – I doubt they do. I didn’t specifically check, but I would be willing to bet they don’t.