I tend not to worry about toe overlap. I wear 44-45 shoes for cycling and it's only a concern on my road bikes at extreme low speed (basically stopped). As far as pedal strikes go, clipless pedals tend to be as narrow as you can get before the meaningful variable is your foot; the SPD system has the benefit of being recessed so you can walk more easily.

The biggest thing I didn't think of when setting up my fixed gear was that your speed is all about cadence. When riding with traffic, I can adjust my gearing to stay within my aerobic ability on a derailleur bike while maintaining the pace of traffic. The only thing you can do is pedal faster on a fixed gear, and you have to keep it up unless you want to get bucked off of the saddle. So I'm mostly slower when riding mine.