If you're bootstrapping, here's my advice (7-figure SaaS founder, bootstrapped):

I wouldn't spend too much time talking to lawyers, but rather just make a simple contract outlining all the things you want to be protected by. Lawyers can be expensive, and still not get the job done right - unless you outline all your terms (might aswell write one up then)

How much to charge him? Well, it's your business :-)

There's no magical number (like someone said $50k lol), but charging someone a hefty fine may be really hard as they can just invest that money and build it out themselves. Make it easy for them to make money, and you'll also make money