The rough rule of thumb is 10lb of shock leader for every 1 oz of sinker weight. So for 4oz sinkers use around 40-50lb shockleader. I use 80lb because I want extra abrasion resistant and I have that in my tackle box.
The knot I prefer to use is the bristol knot without a Brimni twist. All of the guides I have seen online show the knot with a brimini included but i do not feel it is required.
Do not be afraid of short casts, rig often feed in close.