Would be cool. Looks like you installed the original fridge door so it should be really easy to open and close if you want to take a quick look at things. My chamber is the same way and I just pop the door open and take a look inside everyday to make sure all is well. You wont change the temp much inside by opening the door for a few seconds and even if you do the beer in the fermenters isn't going to change at all from a quick peek.
Like I said, the window would be cool but like you said it may reduce your insulating properties. I'd skip it. You can always add it later if you want.