Hi there,
Just to add to the other replies, there isn't really a perfect time to start link building nor is there a fixed number of links that could get you penalized. The focus should be on quality and if you're getting links that are genuine, then you shouldn't have anything to worry about.
As others have said, you should start as soon as you have something worth sharing. If you publish a page and aren't sure why it deserves to get links, then you're going to struggle to get them no matter when you start. You should also remember that not every single page you publish will generate links and this is fine. You may publish one blog post which is very high quality but not necessarily going to get lots of links, but may rank well for a certain keyword. So try to focus on quality over quantity with the content that you create and promote only your best and more link-worthy content.
I hope that helps!
Paddy
But they can provide some context and inspiration for directions to go in.