One of the reasons for going high efficiency is that you can direct vent the exhaust through PVC piping through the wall rather than having to vent through a chimney and over the roof.Chimneys need liners, they can leak exhaust (carbon monoxide) into the living space, they typically are brick structures rising above the roof line (oh and they usually seem ready to drop bricks due to lack of maintenance) ...

No, that's not the way to do it...unless you want to die from exhaustion before you turn 40 (or earlier).  

The other contractor suggested we only need one 5" liner.Is there a ratio of exhaust to diameter that anyone can help me out with?

I personally would take a shot but I have a strong risk appetite (probably should remedy that at some point) but I know that is not the case for everyone and being highly levered can be stressful and exhausting sometimes.

Building had 1 Sewer/Water all other are 2 whole units but because of the water/sewer the mortgage/deed were under both of our names. 2010 This "Friend" stopped payment - I exhausted all avenues on trying to get them out and allow me to take over with no luck.  

I would also suggest an exhaust fan that would turn on when you turn on the lights or put a separate switch for it possibly time delay switch that way the fan would run for 30 minutes or longer.

The above is not an exhaustive list of why Corps make senses - do your research to discover more about their advantages.

I'm exhausted, but I finished writing all the addresses and stuffing the envelopes now.

Even if you are under your 10 mortgages.You will be capped at 10 traditional residential 30 year mortgages.With that being mentioned after you have exhausted your 10 traditional residential 30 year mortgages you will want to look towards commercial financing.

Cabinets on the floor level are shot.Range / Oven does not work.Kitchen floor / sub-floor needs replaced.Half bath needs wallpaper removed and a new exhaust fanFull bath needs wallpaper removed and a new exhaust fan.