A: - All, there is basically no limit. Some older headphone amplifiers had trouble with low-impedance headphones (like in-ears) but there is no upper limit. However, higher impedance headphones will be driven with less power and might be quieter.
B - Most likely, yes. If you want to use the headphones at home and you don't want to damage your hearing, even 250 Ohm should be loud enough.
D - All three sound slightly different. The 32 Ohm is described as a tiny bit more bassy, the difference between the 80 and the 250 Ohm models is practically inaudible. Every reported "difference" might be just manufacturing variations. I think the 32 Ohm and 80 Ohm model will suit your a use at home with your computer.