I ride fixed on the street and ss mtb. I love riding both. I reckon flip-flop hub is the way to go. Try ss first and then move on to fixed. It might be a bit of a shock to the system to go from gears to fixed, break it up with a bit of ss action.

I think there's a belief in an evolutionary process; ss then fixed then brakeless. I don't subsribe to that. I started riding my ss to work and loved it, where normally it'd be my fixed all the way. I don't see that as going backwards or de-evolving.

Is there an intelligent design bike forum?

Try different things, have fun and smile mucho.

Ps. Don't try any huge gears, about 70" is plenty for much circumstances. The lower the gear the better for skips, skids and fly-sh*t. You don't want to spin-out though.

Check out http://sheldonbrown.com/gears/ for your comprehensive guide to gear ratios.