Thanks for all the feedback, everything is really helpful.
-The radio can indeed accept (according to the compatible product list and manual) inputs from the EFIS, one of the reasons why I selected it.
-I decided to go with smaller screens to save on cost, but will revisit later when I'm much closer to delivery date.
-Which certified navigators are recommended for IFR? I'm half way through my IFR rating and will provably will be adding such capability at build time rather than later.
-I have not flow a Kitfox yet, but will sign up for some training soon.