For my “highly used door” I did not use the adhesive. I used two small screws. The sensor is going to stay. I also have a few sensors on metal doors with the standard adhesive, no problem.
As for the 1/8" clearance, that small magnet is the smallest thing you are ever going to find, have you looked at one?
I think you could make this work and look fine. Mine do.
As for the window, have you considered putting the sensor on the top of the bottom pane of the window (assuming a single hung window)? The magnet could even be attached to the glass of the upper pane (inside the sensor), or the side. Just try the sensor and the small magnet to test a few of those options. That small magnet is really really powerful.
Just a few ideas, gotta believe you can find one that works, and looks OK.