The wire from the (neg) battery to the shunt carries all the amps your system will use. Use a table to check the awg size to the length and total amps. Bigger is mostly better.
**edit to add; I don't see a fuse on the cable to the inverter. Nor on the cable to the blue-sea fuse block. Should have something close to the battery bank to protect the cables.
**edit to add; I don't see a fuse on the cable to the inverter. Nor on the cable to the blue-sea fuse block. Should have something close to the battery bank to protect the cables.