I am familiar with job set up (not a total newbie) but a newbie because im still learning.
I have designed and set my tool paths for my project which is 13W x 4.750H x 1.5 thick as I know I need to find my x and y zero but do I need to find my (z zero) before beginning the 3d cut ?
You always have to set Z zero. You set your material thickness but the Shapeoko does not know the spoilboard height. Some people have just the stock spoilboard and others have supplemental spoilboards. So you always have to set Z zero according to the job setup of top of material or bottom of material. However over power cycles the X Y and Z are remembered so if you are doing the same job over and over with the same material height you dont need to set X Y or Z but most people are doing different jobs on every session of use. If you make yourself an L bracket and always put your material there the X and Y are remembered. If you use bottom of stock that is also remembered. But if the stock thickness changes for top of material than you have to set the Z zero every time. Personally I almost always use bottom of material (Spoilboard) so I dont have to set Z zero because it is already set. In the last version of CM the X Y and Z are sort of remembered but only after the bit goes to the BitSetter. Not sure why they made that change but you can cause a BitSetter trip by doing a change tool and just leave the tool you already have installed and the machine will move over to the BitSetter and measure your tool and the last time it was zeroed is renewed/remembered.