Different sizes (40/60 etc) will communicate with each other. You CAN mix generations, but you end up with the functionality of the older one... for example, a W and a W-ES will work just like two W's, but the EcoSmart modes will be unavailable to you. Unless of course you don't link them but run them independently, in which case they all do what they normally do. The EcoSmart modes are meant for at least two, preferably more, pumps together. Nutrient export is ideally suited for one on each end and one on the back. (This info from others; I have W models so I can't vouch for how effective these modes are... but others seem to love them).
Only wireless models (W, W-ES) will work with the Apex VXM module. It acts as the master and all of the pumps are slaves to it.