The key to a high O.G. beer is proper pitching rates, correct amounts of 02, wort-sugar composition, nutrients, and temperature control. I tend to build a nice starter for anything over 1.050 or so. Off the top of my head, depending on your attenuation level you'll need something like 1.100 or more to hit 11% ABV. I don't want to discourage you, but big beers can be temperamental, and you may want to get your brewing practices down before attempting it. If you still go for it, I'd recommend brewing a smaller beer first, racking when finished, and then pitching your big brew right on top of the existing cake....this should ensure plenty of yeast.
As for the hydrometer, I tend to avoid dropping anything glass in my wort for fear it'll drop to the bottom of the pot and shatter. Certainly don't do it if the wort is hot. With cool wort and good sanitation, you should be fine.