Presumably, the energy output from a fusion plant (if we ever get there) should be self-sustaining. For starting up, I’m guessing the plant can draw power from the grid itself, no?
This depends upon the approach. The person you replied to mentioned inertial confinement. If this is used, we'll get pulses that each need to be triggered (with energy gain). Other approaches (e.g. conventional tokamaks) aim to produce a continuous stream of energy.