All the big casinos are going to be busy (Venetian, Palazzo, Mirage, etc) although maybe less so that normal because a lot of people will be there for work instead of play (!) I actually don't care for casinos, but that's Vegas.
Restaurants will be fairly full but there are plenty of choices, so you can go from cheap to very expensive. Most are in the casinos if you are on the Strip, with a few in places like the Fashion Show mall.

-Joe's Seafood Prime Steak & Stone Crab on bottom floor of Caesars forum has a great Bone-in Rib-eye.
-Lux Cafe at Venetian has best Eggs Benedict I have ever had.
-The Pastrami sandwich at Carnegie Deli in Mirage is great if you like pastrami.
-Gallagher's in New York New York is good steak house, And has a really nice Caymus Cab or Silver Oak (can not remember which one) by the glass!

If you go down to Fremont Area and you should see it at least one night if you have never been  to Vegas , Lillie's Asian Cuisine in Golden Nugget is great Asian Restaurant. A few years ago when it only had about 8 tables it was over the top but they have gotten bigger so atmosphere has changed some but Pepper Steak is still really good

Not just during CES but all the major conventions are in January .. and the smaller ones who ride on the popularity of the larger ones.

Its pretty crazy everywhere.

While not an absolute necessity at most places,  it always pays to have reservations.