Toe overlap is a hugely overrated problem. It only occurs when you turn the wheel a significant amount. When actually riding, one turns the wheel very little and uses a shift in weight to take a turn. Shoe size does affect the degree of toe overlap.
As for crank arm length, there are a lot of formulas out there. The one I see repeated the most is inseam (with shoes on) in cm x 2.14 = crank arm length in mm. Here are some websites:
http://www.nettally.com/palmk/crimplic.html
www.sheldonbrown.com/cranks.htm
and so many more...