Some good advice in here!

You're in the hardest phase - 15 until about 60 people. Right now, you are transitioning from needing generalists to needing to hire specialists, but you don't have the infrastructure for specialists. You are likely to start hiring managers now.

Compounding the difficulty, people are going to expect all the services of a 60 person company but you haven't built them, and probably don't know exactly what you want. Have you started getting requests for "HR" to do something yet? Requests for "policies"? In the thread here, people mention documentation. This will be a theme. And your vision for what you want that to look like is important; in my experience if you leave this up to a new hire that's "bigger company" experienced - they will generally rebuild what they have experienced without a lot of thought about adapting it to your company and the size you're at.

Like a lot of startup problems, a) this is a good problem, so don't be mad, and b) there is no magic bullet, you just have to get through it.

My two cents, having mentored a number of companies through this and done it a few times myself, here are my non-negotiables:

1. Keep hiring managers that can execute. It's too early for corporate VP types at your size. And you're probably not ready to manage the political and management skills and needs of corporate VPs just yet.

2. Double down on engaging with hiring - you're likely to be hiring new people with organizational leverage (managers) - you need to be able to explicate the values and make CERTAIN they are being carried out and improved on and broadcast by new management hires; they will be doing things you don't know anything about, so you need to be totally in sync with them. I've read a few startup CEOs that say they stayed personally involved in their first 1,000 hires. That sounds incredible to me, but I like the aspiration.

3. Build reporting process - could be digital could be soft, e.g. periodic standup meetings where numbers are reported - but you're going to need this as you get a bit bigger, and it's culturally easier if it's embedded in the org as you recruit and hire and grow than if you impose it as a "founder/CEO project" later on.

Anyway - what breaks first is your old methods of alignment. A lot of people talk documentation here, which makes sense. Culture is more important than docs IMO.

The way I would say it is: communication becomes exponentially more important. Basically every doubling in size means you will need to say things twice as simply and four times as often for them to get through the org. You will need partners in the org as it grows to help with all this, but you will not be able to give up the responsibility of communicating vision, standards, direction, and to the extent you don't build that skill, you'll send an org spinning, or lose it to someone who is doing this.

Enjoy the ride! It will be fun. Also, things do get easier in many ways as you grow - you get some money to invest inside the company - you'll get to work with great people - it's a lot of fun.