Choosing Vds and id values for a Power MOSFET
During switching, voltage spikes will occur.

Factors which make spikes worse:


fast switching
inductive load (incl. wiring)
bad layout with long, inductive traces
LC ringing
Load back-EMF if you use a motor as brake


This should be kept in mind when picking a MOSFET. For a 100V load, a 130-150V MOSFET should be adequate.

This document explains MOSFET avalanche breakdown on overvoltage:

http://www.vishay.com/docs/90160/an1005.pdf

Keep in mind that fast voltage spikes can also exceed maximum Vgs limit, which is usually pretty low. The very thin gate oxide layer is fragile and will be punctured almost instantly if Vgs spikes above the limit. This can happen on a burst of parasitic oscillations, for example.

Now, the current rating.

Usually, you don't select a FET based on current rating alone. Rather, you'd set a target for the maximum allowed dissipation, and this gives you a maximum RdsON value. Then, you decide on a compromise between RdsON and Qg which controls switching losses, with an aim to minimize total losses (resistive + switching).

Most likely, the FET you will select will have a current rating well above the current you will actually use, and what limits the current will be its maximum dissipation, which depends on how you cool it.

Keep it in mind for short-circuit protection, though.