Bootstrapping with co-founders? I've had lawyers straight up tell me it's probably not worth hiring them to setup the LLC / operating agreement. Just DIY.

Getting outside investment, signing a high value contract, receiving threats of legal action? I would consult one immediately.

I am not a lawyer; this is not legal advice.

When I wanted to file a patent. I wrote the provisional myself and thought I could just hire an attorney to file to convert that to a utility filing. Turns out you can, but it won't be awarded. To get one that's awarded, you have to have the attorney file the whole thing. It's an ugly but widely known secret of the patent law industry.

The second you have a cofounder/business partner you need a lawyer

Last startup I worked for, they had a paralegal/trainee lawyer in house and an external lawyer on a fractional basis.

When the cost of the fractional lawyer exceeds the annual salary to hire one is when you employ one.

Suspect most startups will need a in-house finance team before they need a full time lawyer.