Basically my question was, should I capture at 720p or 1080i to key my footage to make my composition. Fotage was taped using a Varicam, which tapes in 720p. My Deck and Card can upconvert it to 1080i. But, my final output will be 1080i, so in the past I have been capturing and keying in 1080i, but I wanted to make sure it was a better way or not.
As for my workflow being a little off, please elaborate. I would very much like to know. I use AE8 for most of my complicated compositing, and effects. I see more benifits doing this than in FCP.