Re: from three 'double u's to one single 'm'
Technically, W should be double V (and in some languages like Spanish they DO say that--as in "doble ve") As for why not double n, probably because M comes BEFORE N in the alphabet AND a capital M looks nothing like two capital N's side by side unlike with W which DOES look like 2 V's.
PS. Why DOES English say double U instead of double V? Is it because of cursive script where it IS a double U?