Soundproofing Windows?
Just *how* loud is the noise in the space? How loud will it be with the blinds over the windows (does block out some noise)? With the rest of your "stuff" in the room (less echoing)?
Our new place is a far sight better-insulated than our old space. We are right up next to the commuter train tracks, and a block away from the police station/two blocks from the fire station. Guess where they all pass whenever they have to go somewhere? Yup-- within a block of our place, if not right in front of it. And being where we are, there is always some idiot who forgets that "flashing lights on emergency vehicle going very fast means PULL OVER", so they end up blaring their horns RIGHT in front of our place. At least the train is relatively quiet-- they only have the sound of the wheels whooshing, and the little "ting, ting" of the bell as they pass-- unless someone is in the way at one of the two crossings on either side of us, in which case we get to hear the horn sounded.
But even though these sounds can be heard in the treatment room, it's not invasive. I don't know if it's because we and most of our clients live here so it's normal noise to all of us, or if it's just "once in the Zone, always in the Zone", or what, but... it really hasn't been a problem.
Now, when we were renting a room in a multi-service salon, now THAT was where there was unacceptable noise! Chitter-chatter, loud voices not respecting the "massage in session" signs on the door, etc.. I guess the sounds of "life happening, but outside of this sanctuary" is different from "life seeming like it's trying to invade the sanctuary".
I guess what I'm trying to say is, why not try the place out as is, without the sound-proofing, first? You may find that you don't need it after all. If what you want to do is temporary, it shouldn't be much trouble to add it after moving in instead of before. Might come out cheaper that way, too.
Of course, all my words are "moot" if the place is just. too. noisy. So, your mileage may vary, lol. Good luck with it! Congrats on the "way cool space"!