Designing the actual schematic

SOLAR

ALTERNATOR

SHORE

MPPT

DC-DC

CHARGER

POS BUS

BATTERY

DC LOADS

INVERTER

AC PANEL

fuse + disconnect

AC source switching / protection

Main spine

Battery positive -> main fuse -> battery disconnect -> positive bus. Battery negative -> shunt battery side; shunt system side -> negative bus. Nothing except the battery monitor sense lead belongs on the battery side of the shunt.

Sources

Solar array -> PV disconnect/protection -> MPPT -> busbars. Starter battery/alternator -> source fuse -> DC-DC -> destination fuse -> busbars. Shore inlet -> AC protection/transfer/inverter-charger -> AC panel.

Loads

Positive bus -> dedicated high-current fuses -> inverter and major DC loads; positive bus -> fuse-block feeder fuse -> DC fuse block. Negative returns land on the negative bus. AC output lands on a protected AC panel.

Annotation

For every segment record conductor material/type, AWG or mm², round-trip length, expected current, allowed drop, fuse type/rating and terminal size. Add component model numbers and torque values.

Design review

Check energy balance, normal current, fault protection, all disconnect states, charging compatibility, grounding/bonding, temperature, ventilation, service access and future expansion before buying cable.

Rule of thumb

If you cannot state the expected current, full conductor length, protection rating and manufacturer limit for a circuit, the circuit is not ready to build.