>How much time should I spend structuring the project and building tooling to make development easier, vs just diving in and building the project?

Imo, at most 8hrs.

>What are the most important areas to focus on make sure its as useful as possible (documentation, license, community, other areas I haven't considered?

My order:

1. Demos 2. Good README with ability to get started in <4hrs 3. Documentation 4. Community 5. License (If it's supposed to make money, I vote BSL)