real basic questions...sorry

I've had my Media 100 for about a year, and have only used it to cut together a 2 camera church service, it looks great, but no effects outside of titles. Now I'm starting my own business, and I want to get more out of Boris FX 6.0. Here's the question(s).

1. When I just fly a box in with video over another video image, even though it's just 10 seconds, it takes forever to render! It also has a drop shadow. Why is this, and is there something I'm doing wrong?

2. I'd like to fly in several boxes at the same time, so they overlap, and their shadows overlap each other as well. Will this one 30 second scene tkae a day to render?

3. I've read the manual on composition clips, but I just don't get it. Can someone describe how I can use this feature efectively. Any steps to follow? Do you create a clip like I've described and export it as a QT movie?

Thanks for all of your help.