Looking for advice on adapting my mindset

I'm not sure whether this counts as a success or not, but: I went freelance in mid-2018, and by end-2018 had landed a client that turned into long term work, and is about to turn into a growth opportunity: They're one of a large group of clients, and we're looking at ways of rolling out the software we've built as a SaaS.

I need to start thinking about the transition from being a mostly-solo dev, to (potentially) running a small team of devs. I made my first hire a few weeks ago, and already it's becoming clear to me that it's not just a case of simple horizontal scaling.

Are there any good resources, books, articles, or advice on making this transition? I've done lots of reading in the past on things like team/performance management, company culture, etc, but I feel like I need a lot more info - and a few different perspectives, maybe.