Well I've managed to manually install the templates and posted the solution here to Stack Overflow:
As for use, I only use ultimate when I have to :D, for general coding express just starts quicker and is less prone to crashing as Ultimate (but that's just me).
Add as well that I only noticed today that the Phone Express is not the same as the normal C# Express as it's a different executable lol
I think to be on the safe side, I'd install the templates into which ever editions are actually installed to avoid confusion.
As for the side by side dev question above, I'm sure it would be a nice to have.