Ill answer as best I can.

1. You can broadcast as many keys as you like or as few as you like, its easy to set in SB's latest version
2. Yes You can set which boxes to broadcast to (I am currently testing this feature as I didnt have a 3rd machine until now)
3. It works pretty well as far as I can see for simple operations like clicking, but causes problems when you want to drag stuff or move your toon via the mouse.(at least on my setup)
4. No problems to report on stabilty, have a combo fo 2 to lvl65 with no problems whatsoever.
5. No clue, I dont use AutoHotkey, but i think ahk sends keys to multiple clients on one machine, MB just simply sends keystrokes to whichever window is in focus currently.
6. Link works for me. (First post), make sure to get ShockBetas modified versions (Sticky topic) for the server.