Re: single speed bike converts to multi speed?
The problem with freewheels is that they usually require more wheel dishing and they also usually require thinner chain run at angles for some gears.
They almost always require 130-135MM hubspacing, while a typical coaster-brake cruiser is ~105-110.
An IGH allows for a nice straight chain regardless of gear and they are available with the same hubspacing as coaster-brake hubs.
One almost always ends up with a more stout wheel when not running external gears, from my experience.
My Sturmeys are laced 4-cross with 12g stainless Sapims to Weinmann DH-39 wheels. The finest combination of wheel I have ever experienced so far!