Don't know specifically how set up it up in Cadence, but if you are using a SPICE-like circuit simulator, it should be just a matter of reading off the Vdd current. Otherwise I'd assume in a pure digital simulator of modern vintage that this would be an option of any simulation. An opportunity for RTFM.
For the capacitance, again, that's application dependent. To figure out the drive capacity (the upper bound for load capacitance), analyze and create a Thevenin model for the output circuit (its output impedance), define the frequency performance you want, assume a pure capacitive load, and solve the RC time constant for C.
These should be pretty obvious.