The Miche BB is ISO taper, so you're pretty limited on the crank options without spending big bucks. Oh, and for the person who is about to correct me by saying that a JIS crank will just sit 4.5 mm farther in on an ISO spindle, this will bottom out on a lot of cranks (including sugino RD/messenger). Phil wood is also adjustable, but $$$. There is really no reason to do this anyway, you'd have to pull the cranks every time you wanted to change gears.

I'm a little unclear on what you're trying to do here. If you want multiple gears, ride a geared bike. If you want a bailout gear, run two freewheels. The Dos Eno and stuff like that can be used the way you want to, but it seems weird to want to go SS and then do as much jingus stuff as possible to the bike to make it like a geared bike. Don't get me wrong, you can do what you're talking about, but this is one of those kinds of builds that you shouldn't really do until you know a lot more about what you really need and how bikes work.

Also, you will not die if you run fixed, I promise. All bikes were fixed gear for decades and we seem to have survived as a species.