So many companies seem to be organised specifically to create internal silos and barriers between the innards of the organisation and customers. This is a long-lasting hangover from the production line manufacturing party of last century.
How should you be organised? The way that works best for the customer.
Now, when I call Customer Service, I'm calling the organization. I expect to speak to someone who understands me as a customer, who knows the ins and outs of the company and who wants to get me the service I need smoothly.
In a start-up, guess what? Everyone's in Customer Service. So whatever you do, don't create a culture where nobody knows anyone else's business. In fact, don't create a culture where anyone thinks anything is (only) their business.
Sometimes, different roles have different needs. Developers may want quiet to concentrate, while sales people want hubbub. So be aware of those needs... but also be careful not to confuse what people ask for with what works. Because by default, people (if asked) will likely ask for what they think everyone does - create little self-contained bubbles within the organization that, over time, will occupy different rooms, different floors, different buildings even.
I have one specific recommendation for you. While you're small, at the very least have a weekly stand-up, 15 minutes max, for the whole team to say what they've been doing, what they're currently focused on and any roadblocks. That small commitment of time will help stem silo thinking, and help you develop an environment where even when roles may be highly distinct, everyone sees the connections.