So, in Prefect 1 we would attach schedules to flows with specific arguments (ie, "run with X arguments every day at midnight, run with Y arguments every week"). How do we do this with a Prefect 2 Deployment? Does each one have to have a unique name?

Yeah, you could just create N Deployments for your Flow with different schedules. I think Deployments need to have a unique name, but the underlying Flow can be shared across Deployments