That is a fairly standard procedure. You should be aware, however, that Windows handles windows differently than Macs do in this regard; if you have a Windows window maximized then open a new window offscreen your onscreen window will un-maximize - you'll need to maximize that again after you close the offscreen window.
One other thing, you may want to increase you distance offscreen in case of multiple monitors. With the settings you're using if the user has FM on a "right" monitor it would be possible to see the window on the left monitor. Try 10000 instead.