Thanks again.
I'm sorry if I sounded frustrated. I'm not. I'm very great-full for your replies.
No, I didn't want to record live but just thought the preview would be a quicker way to estimate the lighting quality. My plan was to do the keying later. So yes, I would have the ability to undo stuff if a client wanted.
When you mentioned On-Location, that was the kind of responses I was looking for - if a software like that can just give me a live preview. But I also wanted to hear things exactly like you said, like how you can also rely on the zebra and eyeball it - experienced feedback like that is very helpful to me.
I know that eventually, I will learn from trial and error but asking for help in forums like this one lets me educate myself a little more.
Here's something 2 years old that someone pointed me to:
http://www.frischluft.com/lensfeed/index.php
Seems to be something that allows you to preview live video in AE. I need to get to sleep and will check it in the morning but I quickly glanced at the site at it looks like what I was referring too.
Good night and thanks again.