I joined a startup in a very similar position. I ended up taking 4-5% equity, and about 50% market salary. This was perhaps a bit low, as it was barely enough

I joined a startup in a very similar position. I ended up taking 4-5% equity, and about 50% market salary. This was perhaps a bit low, as it was barely enough to get me and keep me on board at the early stages. But the salary went up as we grew, so now I'm quite happy. Also remember this is an early round, and that 4-5% will get diluted a lot as you take more venture. So it's not really comparable to what a future CEO might get.