With a home that age with multi stories and 4K sq feet there's urgent need for a ventilation specialest working alongside hvac contractor at planning stage. All hvac contractors should have a working relationship with one or more ventilation specialest but sadly only about 5% do. It is an added cost over and above the install but IMO return's it 10 fold over the life of system. Between the two contractors they will answer the questions posed here. Meanwhile I'll give my opinions that you might weigh for yourself and ask your contractor about.

The kitchen vent-a-hood and make-up air is more effective and efficient as stand alone. Chance are the vent contractor does kitchen vent installs so they can advise while looking at hvac. I've seen many commercial kitchens where make-up air is pulled in around hood and range where it never leaves before exhusted along with smoke,heat and odors. The kitchen is usually warmer than one might desire but meet's requirements for working in. Energy recovery can be incorperated with vent and make-up system so that kitchen stay's comfortable and little to no conditioned air is wasted. The latter set up is what you need rather than the whole house Aprilaire 8100 ERV.

Getting conditioned air to and from all corners without objectional structrial alterations is always a challange where home doesn't already have ducts in place. Sometimes one or more Mini-Splits to supliment central air look's and work's better than poor and/or unatractive duct runs. I have occasionally solved this with smaller ducts and booster fan inside (especially true for return air). One detail I'm unwavering on is twice or more filter square inches than mfgr's suggested. Doing that alow's more effecient filters without determental effect on air flow. Minimunm of Merv 8 year round and Merv 10-12 at peak of pollen season. The reason i don't suscribe to automated filteration is they breakdown or malfunction with occupants knowing until system is full of dirt that must be cleaned up.

Klem1, Thank you! Ok, since I expect I need to find the ventilation specialist myself to consult with HVAC - who/where do I look for someone like this? Are we talking about a kitchen specialist? As in I should find someone who sells/knows Vent-a-Hood? Or am I calling someone from April Aire?

The goal is both whole-house air quality and making sure we don't backdraft anything when we add that exhaust vent in the kitchen. A separate system for the kitchen is possible, but a lot more challenging with 14in thick brick walls - the only external wall I can vent out of in the kitchen is about 13 ft long, and getting very busy -

it has

1) our electrical meter

2) a transfer switch for the generator

3) a large 4x7 ft window

4) 2 conduits running electrical from basement to attic (because there is no path inside)

5) a 3x4 downspout

6) HVAC condenser lines up to the attic air handler

7) 2 HVAC service disconnect switches

8) a dryer vent

9) an external inline bathroom fan for the basement bathroom (like an external radon fan) (because there was no other way to vent the basement bathroom)

10) the natural gas connection outlet for the standby generator

all on the wall backing the big "utility" pad where there is a mini-split condenser (serves the basement level), the big new HVAC condenser for the rest of the house, and a whole house standby generator.

So finding room for a 6 or 8-inch ventilation exhaust wall vent, AND ALSO find someplace far enough away from everything else for a fresh makeup air supply.... that won't be fun - (which is why I was hoping the ERV on the attic level (with 6 or 8-inch vents on a different 3rd-floor attic gable wall - (also being drilled through 14in brick!) would be adaptable enough to handle the extra load) It's Grand Central Station for the house.

I'm not going to lie, I'm an over-engineer it, DIY everything we can, but try to understand every step if I pay someone else to do something, kinda girl! I warned my HVAC guy I would have read his all tech specs & installation manuals 6 times before he came over. So point me in the right direction! ;-)

So you are telling me right out of the box your chosen hvac contractor is among the 95% that design ducting by yhe seat of pants unless customer go's out and hires someone to help them? Don't rely on companies like April Air that sell add ons to design your hvac ductwork. You will find ventilation specialist in the commercial building trades where their servives are used in every hi-rise,hotel,hospital and other muli-room buildings with 20k sq ft and upwards. Yes,a commercial kitchen ventilation contractor is a good place to start. Even if they don't design hvac vents for remainder of building they work hand in hand with those that do and can refer you.