If your tenant is a good risk and you are wanting to sell, it can be a win-win. I would not try to screw the tenant. Make a fair deal for yourself and them.
If they are a bad risk, don't do it. They may tear up the property, stop paying you and it is a hassle to get the property back.
I'm assuming the mortgage is paid off. If you are wanting a stream of income, I would not overcharge them on interest rates. Because, they may refinance at a lower rate and pay you off earlier than you would like. 4.5% would be a good interest rate for both you and the tenant.
I would get a down payment. It could be 5% more or less. Enough that they have a vested interest in not walking. Enough to pay court costs if you have to foreclose.
You might do a 30-year-note with a 10 year balloon. By the tenth year the tenant should be able to get another loan and pay you off. Or, you might want to adjust the interest rate and keep the note. Consider a clause in the contract that would keep them from refinancing before the 10th year.
Whatever depreciation you've taken on the house, you have to pay this back. Plus, you will owe taxes on capital gains, if there is any. And, interest payments are taxed. You pay these taxes each year on the mortgage payments.
People on bogleheads tend not to like real-estate. It's not a particularly good place to get real-estate investment answers.
the best decision many times is the hardest to do