There is much more to it than that...
As far as I have read, proper isolation window is usually two to three different thickness of glass layered together with film in between. Basically the same as 'bullet proofing' glass. You don't necessarily need the gas or air gap between from what I have heard. But if on the cheap then I suppose whatever works...
And yes the angle mounting is based on the best way to not get a direct reflection back to your listening position. I have seen many studios with just two 1/4" panes. One flat in recording room, and one angled in the control room. That does seem to work, but not the ideal.
Best isolation though is with density. Which involves multiple layers of varying thickness in one panel. Not sure the science behind the layering of different thickness, but it has been documented. I would Google it and try to find where I found that info before I had mine built, but I just don't have time right now. Maybe tomorrow.
If I remember correctly, my window is a 1/8", 1/4", and 3/8" glass, all separated by a clear poly film between. Then sealed to a 1" aluminum frame. It supposed to stop 45 caliber bullets. Not that I record gangsta's, but you never know... lol