Will I work directly with the developer or through a project manager?

Both options work. In a Resource Extension engagement (most common for full stack hires) you work directly with the developer through your Slack, project management tool, and standups, exactly as if they were on your team. In a Dedicated Team engagement we add a project manager who handles coordination, reporting, and quality oversight. In a Project Outsourcing engagement we run the engineering management end to end and you interact with the project manager. You pick the model that fits how your team works.