It is a top/bottom style duplex with a flat roof and a basement so there should be no issues around ducting. each floor is around 1,100 sq ft  Any idea how much I should be looking to get this quoted for?  

If you were to rent to him insist he throw straw down on all the floors.

What is your system for making there is enough money in reserves to service your properties without having to stock pile cash? 

Can pay a flat fee listing service... 

One suggested signing up for their service plan ($20/month per apartment) which includes one annual boiler checkup prior to the winter to avoid issues like mine and small discount on regular plumbing services (50% off of service call charge of $95 and 10% off labor costs after).Is this something you guys would recommend?

The stat is on the main floor and controls both levels.  

I am a Field Service Engineer, I repair/service Nuclear SPECT camera's.

Third, we used real wood floors in most of the living space.

The gas company employees are killing there business here.One thing you need to consider is if the house has enough power service to feed an electric hot water heater, you may have to upgrade that. 

We replaced all the floors with LVP, replaced every outlet, light switch, and light fixture (finding some serious fire hazards along the way).