Carpenters who work on boats are usually highly skilled because they'e often not working with square edges. If he has experience like that, he'd be more than capable of looking after your cabinetry.
I'd hate for you to be prejudice against someone for their disability. I don't think an insurance company could legally be able to be so therefore your liability should be contained within the bounds of anyone else doing the job. If it weren't for this newfound awareness of liability and release, you might not otherwise thought of it, so you can thank him for reminding you to protect yourself.
My brother lost an arm and I can safely promise you that he accomplishes twice as much because he tries twice as hard. But i can also promise you with a fair amount of certainty that if someone has been uprooted from their life and forced to rely on social services - they are going to be fairly desperate. Its got nothing to do with their skill level or personality - its that they dont have enough money to live. My brother is lucky because thats not the case but I would hate for him to be considered a charity case just because he's trying to earn a living. So there's that.
As per payment, I like to get an idea of how much something should cost, less materials (which I usually get myself) and set a payment plan - 10-20% for showing up the first day (which doesn't always happen), another 20-30% halfway through or so, 90% when it' done, and the final 10% a couple of weeks later when the things that nobody noticed were left undone have been completed to your satisfaction. Some people add bonuses and penalties for time constraints if those are of the highest priority. Keep in mind though, that if someone is desperate and inexperienced at giving estimates, they will probably lowball it. That's not good for either of you so get more than one estimate or an example of his working on something so you can get a realistic ballpark figure.
And write a contract for exactly what, where, when, how, and by whom, no matter who ends up doing the work. And if you'e going to hire someone licensed and insured, make sure you get proof of their license and insurance.
It sounds like the man you'e contemplating to have do this work also has some creative and design experience. Don't underestimate that because he may foresee problems or options that you might not. Having been a boater myself, I know that boats are, by necessity, usually well designed.
Best of luck with your renovation.
