Does the upstairs have brick/block partition walls? and which ones? if stud walls with brick bearing walls it changes the work required. Have you had someone check? assuming the balcony is facing the main view they haven't made the most of the view - if you intend increasing window frontage be careful. I assume you are east coast if so the onshore winds means serous glazing - triple may be an idea and ensure the frames are sturdy. You want to get somewhere to hide the beast out of the sea spray coz it'll eat it.