The people who do the work, not the people who supervise it. Project coordinators, controllers, admins, ops managers. Mix departments if you want, the cross-talk is half the value.
The ones you already pay for. The stack decides the curriculum, which is why every session starts from your workflows instead of a standard deck. If a tool is missing, I will tell you before the session, not sell it to you during.
On-site if you can. The room matters: whiteboards, side conversations, the person two desks over saying that report is mine. Virtual works well for distributed teams and for the half day.
Yes. That is the other half of what I do. Some firms train first and hire me for the deep seams later. Some start with the audit and add training when their team wants the skill. Both doors are open.