I'd budget 12-15% combined with repairs.I bet you can get management for closer to 8% on a 16-unit property.Insurance looks very low for a property you expect to be worth $500k.What about water/sewer?

Other than that I would not know where to invest other than staying away from water. 

@Matthew ReumI’m also new to REI but I think that what he means is “capital expenditures” which (correct me if I'm wrong) include new roof, new water heater, and other BIG expenses that don't happen every month.  

There has been a water issue, so that needs to be solved first.

We keep a lock box connected to the water spicket outside in case there is ever a malfunction with the key pad,  so if guests can't get in, I can send them the code to the lock box to use the key.

For example, often fire damage is water damage--they put the red stuff out with wet stuff.

I have seen hot water heaters in bedroom closets but not furnaces.

In the end, water has a mind and power of it's own. 

Have you talked to a local insurance agent.If you're going to get "$750 all bills paid" for each room, why aren't you including electric, gas, water/sewer, lawn care, and cable/internet in your expenses?

Or a pipe or water heater has been leaking for weeks?