To be honest, you're not yet at the scale where this much of a concern. You're either "flat" and about to need to put in structure or you already have it. If you already have the structure in place, then you have at most 4 direct reports and at worst 2 (ideal team sizes being 3-5).

I say this not to downplay the work you've done, but instead to put it all in perspective. You're in the `11-50 Engineers: Clinging to coding.` stage.