We too are self implementing, have about 35 team members and do engineering, sales, installation, manufacture, software, etc. Very tricky when you are highly vertically integrated and have a lot of complexity for a small organisation.
We have people filling multiple roles in the accountability chart. Today I am the CTO, Marketing Manager, CEO and shared services manager (HR, legal, insurances). My COO is also the Sales Manager, Production Manager and Procurement Manager. We are hiring a full time CTO at the moment, but don't expect the accountability chart to change, just some of the names in it.
Almost worth starting with all the accountabilities that you have, and then working them backwards into boxes within the hierarchy