The d and z are seperate, d is the driving part that allows you to drive a straight truck no trailer.
Z is your air brake endorsement, its a seperate course that cost about 250 and is done in one weekend.
You can book and write your d test easy enough
The first part is a written, just like your g1 and about as simple.
You can than go do your course where they will teach you how to drive and most give you a vehicle to do your d road test.
Your z has to be re written every 5 years your d is good for life i believe.
The opportunities open up a lot with this licence
You will always be able to get a job somewhere.
Im a concrete pump operator but i could drive a ready mix truck, dump truck, garbage truck, etc etc if need be.
Hope this helps
John