I'm wondering what is the current average cost, and seeking recommendations/advice.Ty  Are you replacing just the units--no duct work, line set, etc? 

2) How important is it to have a variety of colors throughout the home?

Painting houses a neutral color is the easiest and least expensive way to get houses rented or sold. 

Or keep the uppers and lowers the same and contrast the island color. 

All foreclosures are based on gross fraud, forged signatures,fake documents, corrupted judges who are criminals working for the bankers.The same goes for the attorneys.This country doesn't have the lawyers, and public officials are not following the law.Not the common law not even their own fake, UCC code color of law.BAR attorneys are foreign agents trained to destroy American people and American Constitution!

Studs, plates etc are probably double. if they have the electric and moving the HVAC(duct) in the labor it's potentially not a bad number.

Your air ducts and ceiling fans will be full of lint.  

As long as you follow the rules like lawn maintenance, paint the fence a certain color, keep the house a decent color you'll be fine.

I ask them on paint color, hardware, floor stain/finish etc.

I will spec materials/colors/repair method when I feel it needs to be done a certain way or I want something different/special.