@Mark Johnson, there is a lot going on here and I cannot explain it all quickly so this is the condensed version. 

I like the condensing tankless heaters.

If you have cast iron or convection radiators go with a modular condensing boiler or two from say rinnai. 

For AC, you need separate ductwork for supplies and returns between the units, separate blowers, and you also need separate cooling systems - condenser and coiling coil; you might be able to use mini-split units to achieve that.For hot water, you need the piping separate for the hot water, and then you will need multiple water heat sources with one per unit.

So it would basically take something that might take hours or days for a newbie and condense it into mere minutes.Hope that helps!

The book is basically what every MBA spends 2 years or so studying about cash flow, condensed into 200 or so easily-digested pages.

All units have forced air/ heat, furnaces are located in the basement and each unit has its own outside condenser for AC. 

Get lawn cut, bushes and tree limbs trimmedFresh smellSpend rehab money where you get the biggest bang (i.e. bathrooms, kitchen, paint, flooring, fixtures, etc) vs roof, condenser, hot water heater, etc (assuming they are in at least okay condition to the untrained eye)

I apologize for the way the post was condensed...not sure why that happened.

I have been told that this can very difficult and costly to do due to opening walls/ceilings.(2) Install a mini split system (outside condenser and wall units) for the second and third floor.