You'll never know if there are leaks under the sinks, leaking water heater, excessive damage smoking, unauthorized tenants, etc. if you depend on the tenant to let you know.

Look at the siding many times a problem with aging buildings with cheap TI-11 and leaking windows, roofs etc.

The roof currently leaks around the gutter/soffit area and has rotted some of the truss/ decking/soffit wood.

I had to repair a roof leak+stucco, which cost me 5K this month, plus the dry wall with some mold on it from the leak, which is another $500, so 6K this month total.The tenant kept saying that her AC bill is super high ($650 per month during summer, its  3 story house and the ac is only 2 years old), so I promised her I will buy her one portable ac unit, which is about $300-400Then the AC leaked and I had an ac guy come in and he said the repair will be about $850 (so that is in addition to 5.5K this month) The Ac guy also said the coil needs to be cleaned and the ac filter is filthy.

This is not a minor case of a tenant's car(s) leaking oil on a driveway.

if the furnace dies, the roof gets a leak, how is that handled?

Check for leaks, toilets and sinks.

There was a water leak in the kitchen sink so there was standing water in the basement. 

If one tenant called about a closet slider off the track and another called about a leaking faucet, the leak would be addressed first, followed by the closet. 

It is.Your iPhone doesn’t kill the snakes, unplug the potties, or fix the damage after your guests drag the charcoal grill into the kitchen.