There's nothing at all wrong with Atlas code 83 track. Micro Engineering code 83 track looks a little better but the running qualities for both brands are similar. I certainly wouldn't scrap it if I had it on hand.
If you have the budget, Peco code 83 switches are superior to Atlas Customline switches, both in build and running qualities. They are about twice to three times as expensive as Atlas switches, so the number you need may be a make or break issue. Atlas Customline switches, particularly the new Super Switch line, are still good, useable products, but they will take some work to make them run smoothly and reliably. Many of us have been using Atlas switches for years and, while they may be a little tempermental at first, they work well once they are tuned up.
If you do decide to go with Peco and are going to use DCC, make sure you get Insulfrog type, since the Electrofrog variety has some problems with DCC.