You could do HIIT cycling, but in my opinion its not as effective as an elliptical or treadmill due to the fact you are only moving your legs on the cycle. When on the treadmill, elliptical, etc you are using both of your largest muscle group (legs and back) thus being more efficient.
If the cycle works for you then use the cycle, but there are surely BETTER HIIT methods, in my opinion.
As for the second question I don't think there really is an answer to that...all I know is the formula to find your ideal max heart rate. (220-age)