In iMovie 11, how do I export at my custom resolution/aspect ratio? It only allows 16:9/4:3?
I can address your first question. You can't export into a custom resolution. For that, you need Final Cut Pro X and Compressor. See this blog post for a description of the process.


  (Apple's) suggestion was to edit your video using standard video formats in FCP X, then export it to Compressor and use the Geometry tab in Compressor to create the final movie size you need.