I'm looking forward to trying out your procedure to get Mutt up and running! I don't like the idea though of having the root FS remain writable (and possibly filling it up). Would it not be safer to use /mnt/us even if this means having to login as root? Why do you want to login as an ordinary user?
If you can't make /mnt/us writable for an ordinary user, I'm wondering about the suggestion in the post on installing optware to create an ext2 file in /mnt/us and then mounting that for opt. I wonder if this FS could then be made writable for an ordinary user and be used for the spool folder?