There is no universal employee count that guarantees a qualifying L-1A office. The intended operation must support a primarily managerial or executive position within one year of approval, considering its actual business and organization.
Explain staffing through duties
Show which tasks need to be performed and who will perform them. A small structure still needs a convincing account of management and execution; adding titles without resources or real work does not solve the issue. Link the staffing plan to the business model and budget, and ask counsel to evaluate whether the proposed progression supports the claimed role.
No particular number of employees is specified, and a plan that leads with a headcount has generally started in the wrong place. What matters is whether the staffing described supports the claimed role: whether, within the relevant period, there will be people performing the operational work so that the individual's duties are managerial or executive rather than the delivery of the service. Explain the staffing through the duties.
Set out what work exists, who performs each part of it, and how the individual's responsibilities shift as those positions are filled. A small operation may support the claim where the work is genuinely delegated; a larger one may not where the individual remains the person delivering. Address the reasonable needs of the business given its size, stage and nature rather than importing a number from another case.