The Sahara Tent is a tent dedicated to Electronic and Dance music.
There is also the Mojave and Gobi tents. The Mojave is slightly larger and both cater to rock and hip-hop acts. Arguably the acts that play in the Mojave are "bigger" than the ones in the Gobi, but that's not a constant.
The Outdoor Theater, again caters to both rock and hip-hop as well as larger audiences than the tents due to "bigger" bands playing that stage.
The Coachella Stage or the main stage, also caters to rock and hip-hop artists as well as big name electronic acts. During the day bands that play the main stage could easily play the outdoor theater or mojave, but as the day moves on the bands get bigger and bigger before the headliners eventually come on.
Yes and no. The Sahara always has some sort of dance and/or electronic music. It is the largest tent, and has a big nightclub-type lighting rig in the middle. But that doesn't mean that ALL dance music goes in the Sahara.
The other tents/stages are more unpredictable. The Gobi is the smallest, and the most obscure artists play there. Except they usually book someone in there who blows up right before the festival- Amy Winehouse last year, Gnarls Barkley the year before.
The Mojave is more of the indie-rock tent...except when it's not. The Outdoor Theatre is even more unpredictable. Most of the big "buzz" acts who don't fit in the Sahara will be at one of these two. The Outdoor Theater also often has older or reunion acts who aren't big enough to put on the mainstage, but too big to put early in the day.
The Coachella stage will USUALLY have the top billed three acts of the day in the evening...except when they don't. Occasionally the headliner will play the second to last slot, perhaps if there is a major act closing out the Sahara tent.
Earlier in the day, the Coachella Stage is EVEN MORE unpredictable. Sometimes, it may feature unknown acts very early in the day, in an effort to expose them to more people. Sometimes it's an act that played Coachella before and got a good word of mouth buzz...like Brother Ali last year.
There is also (hopefully again this year) the Oasis Dome and Do Lab, both of which have DJs. Sometimes the Oasis Dome has "celebrity DJs"- famous musicians who do a DJ set just for fun.
But aside from the Sahara, don't count on anything. The Coachella schedule is always full of surprises.