And so I had it done last month (my electrician wanted me to be in town while the work was done - which was a good idea due to potential ceiling troubleshooting implications) - it went as well as it could have gone as there was enough space in the ceiling to run the duct-work/piping (whatever the proper term is) out to the north side of the property without major headaches. 

The major thing to identify with these is the wrapping of asbestos on the metal ductwork.

I was quoted 12-14k for new central heat and air which included all the duct work.

I wouldn't do anything about duct work unless there is evidence of the insulation flaking, then it should be addressed.

HVAC issues-- not just the furnace/boiler but also the duct work design and materials. 

Kilz in subfloors, if it soaked that far, but I am always a fan of replacing where needed, since MDF is pretty cheap.Then if you aren't replacing ductwork and HVAC, then get those cleaned and serviced.  

That was not a great answer to your actual question, but those are the big issues with vac efficiency out side of the unit and the duct work itself.  

The remediation contractor told me that I can just clean it up good w/ bleach water (wearing appropriate PPE) and have the duct work cleaned up and i'd be good to go. 

Opting for multi-zone mini-split systems (link is just a sample, there are many to choose from) offers a practical and efficient solution for heating and cooling an entire house, particularly in renovation projects where space for ductwork is constrained or entirely absent.

There is no ductwork in the attic, but plenty of space for it.