How do you develop quarterly/annual PMM OKRs and tie those to individual projects?

The short answer to your question is that I agree with your approach -- laddering the team up to a larger north star metric against which all activities can be tied is a great solution. I think a simple rule of thumb is, if you’re working on an individual project that isn’t tied to a company outcome, you shouldn’t be doing it. Every OKR should be tied to solving company challenges, and should be measured by outcomes for the business. This is a great north star that keeps teams motivated, even when doing seemingly minute or thankless tasks. 

PMMs need to understand that there is no cookie cutter formula for setting OKRs. The focus I’ve set for PMM has been different in every company, and it all depends on where the company is in its growth journey, and where it sits in the market. Are you struggling with sales efficiency/effectiveness, roadmap prioritization, leadgen, product adoption/customer retention, partner programs, etc.? All of these challenges tie back to things PMM can impact through messaging, enablement, research, and content. And on an even more detailed level, understanding where sales breaks down can help you determine where in the funnel the efforts should be focused.

Ultimately, determining the OKRs and goals I set for my teams starts with a strong understanding of where the business sits, and an understanding of what the challenges are for each product line or business unit. From there, you can start breaking down the goals into strategies and tactics that come with meaningful OKRs that cascade back up into revenue results and business impact.

It's a fun project to take overall quarterly objectives like sales enablement or new feature launches and tie them back to OKRs. In fact today, I was talking with my team about how we can measure success for a sales enablement next quarter. We're going to do this a couple of ways:  

1. Sales confidence -- Are sellers using decks, scripts, etc more (track this through CMS) than they were previously
2. Competitive wins -- what percentage has our win-rate increased from the previous half 

Aside from this, my team currently has a lot of new feature releases. Since new feature adoption isn't tracked through a typical KPI like revenue or bookings, we've opted to track adoption metrics -- how many users choose to 'opt in' for a feature or provide feedback for a public beta feature. From that we can assert a 'win' on a quarterly goal, AND it helps the product team as we build out new features and updates to current ones.