It is completely arbitrary. Arguably, all roles at seed stage or earlier are arbitrary.

Yes, and usually pretty bad salary. I haven't seen any comment mentioning it, but it's another way to get screwed when joining a very early stage startup.

The 1st engineers join pre-series A, get pretty low salary with the promise of making it big when the company goes public or is bought. Then more engineers come on board when the company has more resources after a few other rounds of funding and they get a salary much closer to the market.

A neat thing about the job is you probably get to exercise early and save taxes on your equity if it actually pays off.

But yes, it's not worth that much more than joining a startup later, and it'd be foolish to evaluate it differently. It's fun, but if you don't have real founder equity don't trick yourself into working longer hours than you would at a regular job.

It varies. Co-founder's are "supposed" (according to YC) to have a 10% or larger original stake in the company but people will throw the title around anyway. Likewise founding engineer could be an IC there from the begging with several % in stock or it could be a meaningless puff title.

To clarify: first engineer.

exactly