Digitrax Zephyr Xtra is a excellent starter set, just make sure it's the Xtra a DCS51 and not the DCS50! That is an older version and it does not have the controls to suport the new advanced functions of the new decoders! The main reason I like the digitrax system is that you can add onto it any way you would like, different throttles are available, boosters, controls, computer interface, are all possible and you never have to make a piece obsolete just add to it!
Track can be done several different ways.
Atlas, Peco, and others offer Sectional pieces of track and flex track (36" long sections).
Several manufactures offer EZ track that already has a plastic road bed attached. It's a little less work but it's generally cheaper track.
You want to get Nickle Silver Track not steel or brass.
Code of the track is the height of the rails code 100 you will be able to run anything made, code 83 looks a little more like "real" rails but you will run into problems with older engines, locos, and Rolling stock, the wheel flanges tend to be larger on them.