For the main inline fuse, always fuse at 80% of the rated capacity of the wire, within 2 feet of the battery.
A fuse on average will take 110% - 120% of what it is rated at to blow.
For example 100A fuse will blow at 110A - 120A instead of 100A.
4 Gauge wire is rated for 150A so I would fuse it at 120A or 130A.
All you are trying to do is fuse the main power cable so it cannot exceed its max rating. By fusing it with a smaller fuse you are just limiting your max power & your going to go through fuses like gasoline.
Fuse all other components off the PDB (Power Distribution Block) at the appropriate ratings.
Here is a helpful site and chart for wire gauge sizes & capacity:
Instead of a inline fuse I would look at a Breaker it will end up saving you hastle of changing expensive fuses.
Hope this helps,
MECP Certified & 310k Licensed,