What is the general criterion for selecting a MOSFET voltage and current rating?
The 100V rating is indicating the maximum drain-source blocking voltage that the MOSFET can block when turned off. The maximum current you can pass through the MOSFET is mainly a thermal design issue. You need to estimate the power dissipation of the MOSFET and make sure you can provide sufficient cooling using a heatsink.
When using the MOSFET with a continuous current, the power dissipation is mostly related to the on-resistance \$R_{ds,on}\$ and the current:
$$P_{loss} = R_{ds,on}I_d^2$$
The on-resistance can be taken from the datasheet. But make sure to use the required gate-source voltage. The on-resistance is also very temperature dependent:

Source: IRF540 Datasheet
So you should not only take the raw 0.077 Ohm on-resistance from the datasheet for your calculations but be more conservative. Try to find a MOSFET with a considerably lower Rdson or a relay to make your life easier.