It sounds like key 'organisational' people are being put in place so the organisation can transiton to something bigger. This is a good thing, they're there to support you, as you're the core purpose of the organisation.
Take this as an opportunity for yourself. If you have worked in a corporate environment before, you're probably familiar with policies, documentation (not code, organisational), etc. If not, then don't worry.
This is you're chance to shape that from the start.
If you're the owner of a product or part of a product, you have a lot of leverage and power, just don't use it recklessly.
For example: I joined a company with no job descriptions. When the expansion came, I got to write my job description. My department (me) had no Statement of Purpose, so I wrote the Statement of Purpose.
We also had a training course on RACI (basically, a simple way whenever undertaking a task to make sure who is Responsible, Accountable, who should be Consulted, and who should be Informed). It's a simple idea, but well worth keeping in mind whenever doing something because an expansion means the amount of people that need to be 'in the know' changes (in my case, from casual chatting and word-of-mouth) to making sure things were documented in emails. It was different, but it helped.
The good thing is, you're in expansion mode. That means a lot of stuff can flow to you if communication well.
Don't appear self-conceited (not saying you are, just don't appear like that) by getting withdrawn. Given your company was small, the boss or VP is probably close, so let your ambition (be it a specialist, manager of a product or part of a product, etc) be known to them.
Things can stay casual and personal, but with more and more people, things will go wrong if issues don't get documented and followed-up more formally (from feature changes to un-communicated personal leave), simply as there's many more people who will be out-of-the-loop and uninformed of events.
The transition phase was the worse for me, as others just didn't get it. There'd be a face-to-face conversation I'd not be involved in, because others were used to the 'old way' and then things would escalate because someone key was out-of-the-loop and I'd get a question from the GM 'why was this not done?' It was a pain. But you can get through it sooner if you adapt sooner.]