You should not accept this contract.

You are being asked to accept liability for people without an incentive to deliver good work of whose reputation you don't know.

The more unspecified the liability and acceptance/delivery or services description is, the more likely you are to end up with an endlessly "unhappy" client who won't make more payments but won't say it's all finished.

I suggest you run. Never take liability without responsibility, especially not without any large upside possibility. In the absence of clarity, clients will try and argue that you own the liability because you directed other people for the final product. You want to specify details and work against them with a healthy 20% buffer of extra quality/work to make sure the client can never argue you didn't fufil the work. This is the opposite of that. Don't do it.

Reject all liability. Software is almost always sold as-is. You should stand by your work, fix defects, offer help, offer advice, be a decent human, etc. But that should be done as more hourly work. If they are unhappy with how it goes, they might never hire you again, but that does not put it on you to be liable for their operations.

So you are already in a good place - hourly rates, define and communicate the specs to the other devs, and reject liability. If the client says no to that, walk away.

Larger clients will often require you to have liability insurance. I was able to get some quotes for this as an independent consultant myself. However, given the extra expenses you'll have to charge more. I'd suggest using this higher cost as leverage toward the liability they want you to accept (for you, ideally as-is). I'd also explain since it's hourly if they dislike your work they can just replace you.

IANAL but my understanding is that for contractual work in the US you can only realistically be sued for at most the amount of the contract (supposing non-negligence). Asking you to accept liability beyond this sounds risky.