(1) The only +2 well that I've used regularly is the Luck well in New Sorpigal, and I've not used that regularly enough to be specific about the recharge times. I tend to go back and top up when I've finished doing something else, and the elapsed time depends on what the "something else" was. But what you say fits with my experience.
(2) I'm pretty sure attacks on a sleeping party are random. My experience is that if the immediate vicinity is reasonably monster-free, you should get away with an undisturbed night's sleep more often than not.
(3) This agrees with what I've found – and item "of x magic" will not stack with a different item "of x magic", but will stack with an artifact which works on a range of magics that includes x. Items "of Power" stack – each one confers 5 levels. I've never been able to tell about Thievery because I know of no way to put actual numbers to the benefits obtained. However, my archer (which I use as my thief) at Master Disarm and equipped with both Pendragon and Hades cannot reliably open the "difficult" door in the entrance hall of the Superior Temple of Baa.