Elementary questions about transformer design

Hi,

I have a relatively superficial understanding of transformers (and magnetism in general) so I was wondering if you good folks could shed some light on a couple of simple questions.

The elementary transformer theory that I'm aware of states that the ratio of voltages across the primary and secondary windings is equal to the ratio of turns in these coils.

The first obvious question is; why doesn't a 2:1 transformer have 2 turns in the primary winding and 1 turn in the secondary winding. Why stop at integer numbers of turns? What about 1 turn in the primary and half a turn in the secondary winding?

Obviously there is some sort of magnetic coupling efficiency related to the absolute number of windings in each coil, but I don't really know how this works.

A follow on question would be; What determines the quescient current that the primary winding sinks (whilst the secondary winding is unloaded)? How is the impedance of the primary winding determined? Is the impedance of the primary winding simply the inductance and linear resistance of the primary winding when the secondary winding is unloaded? Does the impedance (inductance) of the primary winding drop when the secondary winding is loaded (thus allowing more current to flow through the primary winding?

How does the current flowing through the primary or secondary winding affect the supply (output) impedance of the secondary winding?