How do you calculate the ideal mechanical advantage of a lever?

It's 1. IMA = Distance in / Distance out. A single pulley doesn't do anything toward mechanical advantage, it changes the direction of the force.

Not always. A single-axeled pulley (the typical pulley) has an IMA of 1, having one axel. If there was a second axel, then the IMA would = 2, so on and so forth.

The easy way to do it is IMA = # of axels.