Insurance: you need landlord insurance, basically liability + the house. Tenant can get his own insurance for contents of the house, unless you're renting it furnished. At least in my experience for a single-family, it's the same price or slightly cheaper than owner-occupied insurance.

Mortgage: depends on the terms of your mortgage. Don't ask/don't tell might be a solution if you feel you can get away with it. With other mortgage problems being rampant, if you're making payments on time, this will be #57435346356 on the bank's worry-list.

Fireplace: can you find some elegant means of locking the doors down?