I nice new, Headunit would be a nice start...don't worry about an AMP unless you are looking to add a lil more power to after market speakers or subwoofers. Usually a decent headunit and after market component speakers sound nice.... Wiring usually isn't too hard if you have the wiring kit...but I usually ghetto rig mines by just matching the colors of the wires....but I think it's best you get someone who knows what they are doing to do it for you....
Basically it just comes down to how much money you are willing to spend..