Great questions.. I find whenever you are applying a commercial or retail element into a residential project everyone seems lose their minds and talk negatively.. Yes everything is possible.

-You may not want to insulate the hallow aluminum mullions with spray foam as it may not function correctly, and removing a broken glass panel would be very difficult... In this project (located in Minnesota) we insulated the mullions using batt insulation.. believe it or not it has been very helpful on keeping the cold out!
Note: some mullion manufactures have insulation elements pre - manufactured for their applications... Think of all the LEED certified buildings out there with curtain wall systems.. In order to obtain their classification they must be insulated (one would assume)

-we did not install any additional flashing for these windows as it was not necessary. Make sure you consult a few vendors (mullion and Glass installers) to make sure your GC installs them correctly! The last thing you want are Ice Dams, water leakage issues, etc.

Hope this helps a little..

Thanks, I appreciate the input. Today I had them come by again to get some final measurements because I told them I wanted my windows to look like the image I am attaching.

Notice in the image that you see the full frame of the windows. They suggested to break out the wooden frames the current windows fit into and to install the curtain wall brick to brick. Of course this will cost more money and the windows will be even larger.

How to I get the drywall to come up to the window frames with out over lapping them?