1. Talk to a lawyer who can write you a proper licensing agreement.
2. Charging should be around $10,000 per year or $50,000 one-off fee if you are scarce for money. It could also be $50,000 per year though, but this depends on how big of a budget you think the licensee has. Try to find that out indirectly in a call with them.
3. If someone can only pay you $5,000 per year or less, I wouldn't do it, since your rebranding, bugfixing costs are higher than the $5,000.