I have removed old cast Iron tub and want to replace with tub and surround however, there is a picture window right in the middle of the would be surround. I am fairly certain I should board it up as the surround seems rather difficult to work with . I have had several people tell me to tile around the window and or cut the window out of the surround. I am not sure which is the lesser of the two evils.? Thanks in advance!

Many have a window in the bathroom. Some actually use them, most don't. It is a good place for water to run down the wall and rot the wall behind the veneer. If you are going to not leave the window exposed then completely remove it.