[7Figures2Commas]

I will refrain from commenting on the equity other than to reiterate that what you've described is highly atypical for a "real" startup and if you're seriously considering the offer, you could do a lot worse than to discuss further with experienced counsel.

As for the salary, ask yourself: how long will this company be able to make payroll with nothing more than "car money"? The all-in burn on you alone will be in excess of $11,000/month. Even if you assume that the four other roles are filled with folks who will work for peanuts (not likely), it doesn't sound like the company currently has more than a half a year of runway, and that's probably being generous. For all you know, the founders, who you say have full-time jobs, might be putting money into the company on an ad hoc basis and could bail after a month if they lose interest.

Frankly, in my opinion, barring some major details you've omitted, this offer sounds like you're being told you won the lottery but have an incurable illness and two months to live. The fact that the founders are still employed elsewhere, aren't being forthcoming and have audacious, unrealistic expectations about valuations and exits before they even have a product are huge red flags.