Only these type of requests (water leak and no heat are urgent) and then you should text/call (your preference).

So I analyse each property individually, looking at major features like roof, heating, cooling, hot water, anything likely to break down really. 

Or is the landlord always responsible for the water bill and heat?

The heat is problematic.

Last week this tenant casually informed me by text that he had hired a heating guy to service the furnace of the building that is in his half of the duplex.

What's important is secondary security locks, AC/Heat for all living sq footage, all working outlets, damp rated bulbs in bathrooms, working appliances, fire extinguishers, we do 1 year worth of monthly air filters, which cost way less than ceiling fans, working fire alarms, etc.Best wishes, good luck.

Does the garage have proper firewall protection and heat alarms for whoever is sleeping there?

Only heat.

The area's you've identified are begin to heat up. 

I go over there- and her heat is off.