As an entrepreneur myself, I know how difficult this can be :( But there is hope! :)
Keep in mind:
An organisational structure is never a solid and completed piece of work. Moreover, it remains flexible and adjustable as you grow and add new team members.
To get started, I would suggested the following approach:
(1) Determine whats already in place
Take a closer look at which positions are currently set and which roles will be needed in the next 3/6 months.
(2) Define which kind of organisational structure you wish to have
Hierarchical structure: A tall structure will have many different levels of employees all reporting upwards to team leaders and then up to operational management.
Flat structure: Flat organisational structure has fewer layers of management and wider spans of control. This means operatives can access and communicate with managers more easily and quicker. As a startup, this is what you want to achieve.
(3) Fill the typical top 5 roles, for example: (Depends on the type of startup)
Head of Engineering
I hope this will give a better overview of how to tackle this situation. Please let me know if you have any further follow up questions.
Here are some interesting links: