Having been through a very similar situation, here are a few ideas:

- Get a good lawyer, it seems expensive, but is cheap compared to getting a bad deal.

- In deciding between cash vs. equity, a useful way to re-frame is "If I had it all in cash now, how much equity would I buy at this price?"

- The CEO has much better knowledge about the company, and an offer to buy may be a signal that there's positive information unknown to you.

In my case, I refused the lowball offer though the amount of cash was tempting, figuring they were making an offer for a reason. A few months later, I was offered 4x the price as part of a funding round. I took it without further negotiation, since that was enough to make a significant lifestyle change.