Regardless if you decide to move forward or not, I would highly recommend you approach it like finding a co-founder.

It sounds like he wants you to stay on after the fact, so your future liquidity (and employment) is going to be dependent on him.

So, be sure to ask yourself
- Do I know him well enough to make that kind of decision? If not, spend time with them.
- Do you trust them? Listen to your gut.
- Will they teach you things? Do they inspire you ?

If any of these are no, then dont even bother.

The most likely outcome is failure, so ensuring the journey is done with people you actually want to spend time with and trust is paramount to anything else (price, etc)

Open to a call if you need to discuss.