From which point does it become dangerous to keep going as the sole developer on a project? [duplicate]

This question already has an answer here:

• Working as the sole programmer at a non-tech company 8 answers

I'm currently working as the sole developer in the brand-new "software department" of a company that, for the moment, gets all its revenues from consulting. The idea is that the management wants to capitalise on their consulting experience to offer quality software to their (already existing) customers, and expand from that to become one day mostly a software company.

This sounds perfect to me, like a rational and realistic plan. So they hired me. But now I'm beginning to feel that I need a proper software development team (back-end + front-end developers, UX + UI designers, testers...). Currently I take care of all this by myself and it works well, but the technical debt is growing.

The two projects I've been working on for the last 5 months sum up to approx. 15'000 LOC (1/3 Python, 1/3 CoffeeScript, 1/3 css-html). All from scratch. It consists in two web apps based on Flask and d3js. I don't find it overwhelming yet but I feel it will soon become unmanageable if a proper team doesn't get involved.

What do you think about this? Do you think it's pretty normal and that quality work can be done further this way (sole developer for projects of this size)? Or in your experience, would it lead to a disaster to keep going on like this?

Also, what could be said about a moment in time when it's the most appropriate to get a team working in a project's early life, before being to early and after being too late?

Any thoughts appreciated.

Note: I know this could be flagged as an opinionated question, because obviously it is. Don't hesitate to suggest another Stack Exchange site if it's more appropriate.