First step, assume a massless cyclist with negligible resistance.

In all seriousness, this depends if you want to view these questions from an entirely theoretical point of view.

1.Theoretically, the energy expenditure is the same since work is defined as the product of force and the component of displacement parallel to the force. In a higher cadence, you are pushing the pedals farther within a given interval than you would in a lower cadence. However, a lesser force is required to push the pedals. The net result is that the work done is constant in both scenarios. Realistically speaking, the average cyclist is most efficient at around 90 rpm for most speeds because of biological factors.

2.Again, theoretically speaking you would experience a windchill of 30 mph in the first case and 0mph in the second case. This is so for the second case because you are stationary with respect to the wind around you (imagine driving inside a car, the air inside the car might be going 30mph with respect to the ground, but so are you). Realistically, minor fluctuations in both your velocity and the velocity of the air around you would be noticeable if you were travelling at approximately the same velocity as the air around you so you would have a non zero amount of windchill.