Be conscious about governance, not formalGovernance is important. Your project does have a governance model even if you don't think about it or if you don't write down the rules. It governs how your project will work and how people will be able to collaborate. It will also define a big part of your culture. You don't want to leave these things to chance. So be conscious about governance.
That doesn't mean that you have to write rules and policies for everything. Often a healthy culture where people learn by following the example of the leaders and other members of the community works well. It might be tempting to create a formal structure to cover all kind of possible scenarios. But creating and maintaining policies is an expensive process. Don't be formal where you are not sure it's needed.
Spell out the fundamentalsThere are some non-negotiables which have to be spelled out and written down. The license is the most important one for an open source project. You also might want to spell out some other aspects which define your culture such as values of your community or a code of conduct.
Learn from othersThere is a huge number of open source projects out there. They cover many different use cases, types of technology, and flavors of community. Learn from them. Most things have already been invented.
Don't create foundationsYou will know when to ignore this advice but generally don't create foundations. It's a lot of effort and needs ongoing work to keep up with the responsibilities and obligations you create by that.
There is a number of umbrella organizations your project can join. This gives most of the benefits of having an own organization such as being able to handle money but with much less work.
Beware of growthDifferent stages of an open source project need different types of governance. Growth will change the dynamics of your project. Be conscious and watch out for changes in the project which require changes in the governance.
Also think about if you want to have growth at all and what kind of growth. Having many users is great but it also comes with responsibilities and expectations.
Keep your sanityYour are working in the open. A lot of what you do is public. People will contact you and will want things from you. This can be overwhelming, especially if your project is successful. Find ways how you keep your sanity, how to avoid being stressed out by your open source work, how to keep a healthy balance between your open source work and the other parts of your life.
Be kindThat might be the most important advice. Be kind. Be respectful. Be aware of cultural differences. Make sure that people feel well and are happy in your community.
It's software development. It's all about people after all.