Noob questions here:

Can optional deployments be resolved during the deployment step of the Status phase? E.g. A Dark Power

Can a group also be a single character deployment card? E.g. Hired Help

Yes. The deploy/reinforce step of the status phase is the most often happening optional deployment. You can also reinforce during optional deployments.

(The "optional" because you don't need to deploy or reinforce anything if you don't want to.)

Each deployment card and hero is a group, even when there is just one figure.