I'm down here, so maybe I can help a little bit.
As for food, depending on what you're willing to spend, you have a ton of options on the riverwalk.
For breakfast, what I'd definitely recommend is Las Canarias in La Mansion del Rio. It's a huge buffet - amazing food - but pricy. Worth it, though, but I wouldn't do it every morning. Cheaper places down the way with good food as well.
If you're there for a few days, also try the Guenter House. Off the Riverwalk, probably about ten minutes away by cab - but they'll all know where it is. Indoor/outdoor place at an old house in a flour mill. Great waffles, pancakes, biscuits and gravy, fresh fruit, etc. Not too expensive, either.
For regular meals, there's a great restaurant called Boudro's. A Bistro type.
http://www.boudros.com/boudros/
Paesano's has great Italian food. And for Mexican food, I'd leave the riverwalk and go to the Market Square to, as has been mentioned, Mi Tierra or La Margarita. Owned by the same family - both in the market.
Biga on the Banks is a really good restaurant, too.
www.biga.com
There are some good restaurants in the Hotel Valencia of which I'm drawing blanks on their names. If you haven't booked a place to stay, I'd look at the Valencia - a very modern hotel (
http://sanantonio.hotelvalencia.com/san-antonio-riverwalk-home.php), the Watermark Hotel - which has a full service spa for the wife, La Mansion del Rio - an old spanish feeling hotel. Or the new Hotel Contessa. All of them are on the quieter end of the riverwalk.
And there's Sushi Zushi, if you're into that.
If you have kids with you, there's Hard Rock Cafe and The Rainforest Cafe.
As far as Fiesta Texas tickets - HEB has them, but you can get them at the gate with no real problems.