I may suggest you – first of all – to read Chapter 9 Section 1. “Organizational Structure: An Overview” https://ctb.ku.edu/en/table-of-contents/structure/organizational-structure/overview/main
Take a look also to the other sections of the same Chapter, the Checklist and the Examples.
I don’t know the field of action your organization will be involved in, so it is difficult to give you more specific advice… About legal documents: legal rules may be different in the different local areas. Perhaps you have to ask a consultant with expertise in non-profit organizations. It is the more reliable help for you in a crucial time as the beginning of an activity. Or, meanwhile, you can look within nonprofit organizations in your context for someone who may be a “peer-support” for you (and who might be also a future partner for your projects).
Many wishes for your work!