[procaryote]

Deciding what to work on is critical as you say, every startup I see have at least 10x the things they want to do compared to the number of people.

But you're working in a pretty well known area. You don't really need planning for all 1000ish people as you could take this well known area and divide it into pieces that are largely independent. These pieces are either just table stakes where you need to be good enough but not innovate, or they're part of your vision for how to differentiate from other PaaS companies. You can budget accordingly and let these pieces do their own planning with their importance for the overall vision as context. (If you don't have a vision, your company is probably a mistake. Why are you even there?)

If there's an area where you don't need to innovate much, but you need to catch up, they might actually do a 3 month plan. If there's an area vital for your vision, they are probably trying new things, learning and re-targeting. Three months is far too long to plan for them on a tactical level, and probably too short to actually deliver on the vision.

You can certainly have a quarterly checkup or something to see that all parts are working from an upper management level, but the useful planning horizon varies by problem area, and they don't really need to plan in the same way.