Welcome to the forum, and don't worry, I've seen worse English.
Regarding your questions:
1. I guess you're talking about the famous Winged Hussars? They were indeed one of the finest cavalry units that ever existed, but I'm not sure they're identical with the Hussars in this game.
Anyway, changing unit stats is intirely possible and won't mess with your game (you must have made a mistake the last time, I have never had any problems after editing the EDU). This link should help you finding out what you have to change:
http://www.twcenter.net/forums/showthread.php?t=221093
2. I find the cities/castles ration in central Europe to be reasonably balanced, but I have never played a late campaign with France so I'm probably not the best judge.
3. I know that problem and there isn't much you can do about it, I have never managed to make the AI attack a mutual enemy when I wanted it. I guess you'll have to watch the diplomacy screen and wait until they declare war on their own account.
4. Yes, that is possible, but only by heavy scripting. Maybe there are some submods that have reemerging factions so I'd advise you to take a look in the submod section.