What's your framework to prioritizing needs/deliverables when you're the first Demand Generation manager at a company establishing the function?

A team of one has the opportunity to lay the foundation for a solid demand generation function. That being said, it's important to ensure a thoughtful and scalable approach. You'll need to choose 1 or 2 main KPIs to impact, you should work with sales and PMM to form a point of view. You might choose traffic and form fills to start depending on the maturity of your business. Or you might choose MQLs and Opportunities. Once you have your KPIs identified you can begin crafting the right mix of programs to achieve your targets. Generally speaking I recommend an 80/20 split, 80% always on programs, think trial, ebooks, on demand webinars, AR, etc and 20% point in time (PIT) live webinars, training, hands on etc. Especially for a team of one you need to prioritize programs that will help you get the most out of your efforts. You’ll never be able to run enough webinars to keep up with growing targets, so it's important to build a solid always on engine and supplement with PIT. 

In order to prioritize needs/deliverables you first have to understand the associated goal(s). Based on this, you can work backwards to better understand what will drive the desired outcome.

It’s easy to quickly become overwhelmed as the one demand generation manager. Prioritization is key. Ask questions about deadlines. Be sure to have a solid understanding of scope while also managing scope creep.

Lastly, it’s important to clearly articulate blockers, dependencies, and set realistic expectations.