I ran a 215-40-16, it was quite the low profile. 225-50-16 is a popular size. Your fitting these to a 280zx? I cant give an accurate guess whether they will fit a ZX or not.
Most times offsets are listed, + will cause the wheel to be more sunken into the fender, closer to the struts, more inboard, whatever you want to call it.
When an offset is listed with a - , that will mean the wheel is more outboard, has more dish and sits flush with the fender, or sticks out past the fender.