I am planning a shoot, which will finally be mastered to HD, but I want to shoot and work in 4K, and use the extra resolution to put in zooms and pans in post.
From the research I've done though, it seems that the work flow for using 4k files in After Effects involves going through Scratch on a PC.
Is that correct, or is there a work flow for the Mac that will work.
After Effects supports DPX I believe, so there's no reason you couldn't use DPX sequences in After Effects on the Mac. Use FCP to edit with proxies, then use Crimson to generate DPX sequences from your edit.
I'm not sure I'd try. I'm also not sure there is any real benefit to working at 4K that long when finishing for HD.