ADS should be fine for creating the layout, many people use that.
If your PCB has solder resist layer, you need to define that layer in your SMD footprint.
Regarding layout parasitics, you can do EM simulation of the overall circuit (most accurate, but not so easy to get started, many details to consider), or include the pads as circuit simulation models with the pad size specified. This give the correct shunt parasitics.
To get the right amount of series path length, you would model the pad as a piece of line (to component reference plane) plus some open ended stub. The physical size of the diode itself is already included in your model (the series inductance). What you need really depends what you required level of accuracy is, and how much which parasitics matter at your operating frequency.