1) It is in Fair Park, the annual site of the Texas State Fair (the musical will be going on during this year's State Fair, so the place will be packed with people/games/rides/food. It is a little southeast of Downtown Dallas (I presume that is what you are refering to as "the center of the city"). There are a couple of restaurants/cafes around Fair Park, but the area had fallen into blight for about 50 years, though some redevelopment steam is beginning to develop. I would recommend staying in Downtown and hiring a car to take you to and from the theatre (or the Fair, perhaps, if you want to experience that as well. It's pretty fantastic, and I think your show ticket will get you into the Fair as well). Then you could eat at any of the numerous specialty restuarants in or around Downtown Dallas and will be near the light rail and streetcar for any additional activites you might want to do in Dallas.
2) There are tons of hotels in the area. The most 'posh' is the extremely expensive botique Hotel Zaza (
http://www.hotelzaza.com/ - they also have a fantastic "asian fusion restaurant, Dragonfly, that is not as expensive as you might expect). This is where Jessica Simpson always stays when she comes to town: there was evidently a bit of a 'war of words' there when both she and Brittney Spears stayed there. It's a fantastic hotel, but it can be immensely costly.
Another option would be the Crescent Hotel (www.crescentcourt.com). Also very expensive, but older, and a little more "traditional Up-scale New York" in style than Hotel Zaza. It's my favorite hotel anywhere, period. Rates go anywhere from $225-$3000 for the penthouse suite. It's connected to some of the most upscale dining and shopping places in the entire area, perhaps the state, and right by the trolley line (across the street from Zaza, also, so they both have excellent locations).
Other pretty nice hotels in the area, that are much more affordable, are the Adam's Mark (
http://www.adamsmark.com/dallas/index.asp - 1,840 rooms in what used to be an office skyscraper, right next to a light rail station, so also very well connected), The Fairmont (
http://www.fairmont.com/dallas/ - Very nice inside; fancy, Italian-style rooms that on average go about $200 a night), or more traditional chains like the Hyatt (direct connection to Union Station and the rotating restaurant at Reunion Tower), Hampton Inn, Embassy Suites, etc.
3) The tickets cannot be purchased yet. The DSM likes to get as many season subscribers as they can, so they often wait until a month or two before the run of a show begins to sell invididual tickets. You could call their office and ask when tickets to Wicked will be available, their website is www.dallassummermusicals.org
This is probably alot of information, but there is a lot more that is available if you need it. Feel free to visit the DFW Urban Forum (
http://forum.dallasmetropolis.com/) and ask any kind of question you have about accomidations, activities, transportation, restaurants, etc. I post there often, but I'm no where near as knowledgable as most people on that forum are. If you have any other questions, feel free to post it here, email me, or post questions over at DallasMetropolis where I and others will rush to help you.
Good luck!
I think there is a definite improvement. It's hard because I was at the very front where the sound has always been pretty decent. I'd have to hear it from the back orchestra/balcony to see just how good the new system is and see if it has solved any of the echoing problems. Are you seeing the show? The cast is very strong and I had a WONDERFUL time. There is one performer that I'm still not sold on - but overall I didn't have any complaints. Solid production. 
