Indeed iMovie is a great work environment. I love it myself.
One thing to keep in mind though is that iMovie is "DV format" based, and QT Pro and Final Cut Pro are QuickTime based. So if you import content into iMovie, edit it, then export it to QuickTime for playback, you wll have some quality loss, especially noticeable in still images. It's not bad at all for titles and soundtracks however.
This isn't a deal breaker, as you've indicated in your note. If the quality of your original images is very high, you can have a little loss and folks won't notice -- a reasonable tradeoff for iMovie's convenience.
You can also bring another application into our ad hoc IDE, Totally Hip's LiveSlideShow. It's a wonderful program that gives you much of the power of iMovie, but it's QT-based, so the quality is very high. You can smooth any rough edges in final production with QT Pro, and look like a champ.
Bottom line: lot's of ways to do stuff here. I appreciate all of these great ideas.