Hello, I'm looking to change the window in my bathroom (getting a little rot). Hoping to install a pre-fab glass block window, but I'm not totally confident in sizing and would like to double check before I order. The width, as measured from the outside, is 32" from siding edge to siding edge, and the height is 42.75" (measured from red to red edge on the outside of the house in the picture, and nearly the same from tile to tile edge from the inside). I believe I should then order the next size down from this, and was looking at this one: Clearly Secure 31 in. x 40.5 in. x 3.125 in. Vented Wave Pattern Glass Block Window-3242VDC - The Home Depot It also comes in 31 x 42.5" and many others. It's hard for me to tell what I will need to remove before actually cutting/ripping into the window. From what I can tell, the "rough cut" opening is basically everything between the siding pieces, and that's what I should measure. However, part of me thinks I should be ordering a smaller size, because I won't want to remove all of that wood between the siding? Thanks in advance!