To name a few:Wall modification and drywall patching for new ductwork locationsFloor plan modification - You will need to build-out of mechanical closets to house the furnaces for each unit which will alter the floor planA/C - Not sure what the existing cooling system is, but the new heating system could effect the cooling systemElectrical - May need new electrical panels to accommodate the furnace load, & wiring to power the new furnace unitsWith that said, I think this could easily cost over $5,500 a unit when you consider these additional scopes of work.I would highly recommend getting in touch with a local HVAC contractor who can provide some insight on the construction considerations & costs as apart of your due diligence.

I used to work with some that would replace the roof before installing the panels as part of the deal, and they had good financing.

Hello,I'm looking to build a duplex in Los Angeles and am researching panelized wall systems in steel or wood. 

They had stapled over the hole a ugly piece of paneling.

The hot water heater will be 220V, so you will want to make sure you have an updated panel and have the room in the panel or at least have the budget to update it.

I closed on the property a couple weeks after.Some items off the SOW include a new roof, new windows throughout, electrical and plumbing rough-in, new kitchens and bathrooms, move the 2nd floor entrance to new location, sidewalk repair, 200 AMP panel and separate electric and gas meters, forced air heating, and new 12 mm laminate flooring throughout, among other items on the 3-page list.

My question for this panel is this a widely accepted practice among investors, or a lower percentage of people who see this as a wise thing to do.

You mean solar roofing or solar panels on top of the existing area?

Stained wood plain doors throughout, and they put a white panel door on. 

Is the panel grounded correctly?