For a previous role at a fintech company, we did have a CTO and a few engineering managers managing each of the various tech teams. In our organization, we had web development, operations, integration (which builds development tools and sets up testing infrastructure), internal development (builds admin tools), product development (consisting of web, mobile and other business-specific dev teams)

I think the necessity of the CTO depends on the technical savyness of the other executives although an effective CTO will always be able to highlight challenges the tech teams are facing, lobby for resources when necessary and provide sufficient support to make sure the tech side of things is working well.

3 co founders , one of them acting as cto for 6 people dev team , other 2 co founders do legal and marketing. Below 3 co founders we have 3 managers managing a support team (they also do support themself). We do not have sales , growing organically for now.

I asked about org structure options for growing companies recently, but didn't get any responses: https://news.ycombinator.com/item?id=15006425

Hope this post has better traction. Look forward to the answers.

How big are you, and what are the cofounders core skills?

Getting a 500 person org setup founded by 3 lawyers would not apply to a 3 person startup founded by engineers.