My confusion is if you have to go up in fuse or breaker size when you go up in battery AH size?
Fuse ampacity is based on the maximum load.
For most systems that is the continuous rating of the inverter.
For you setup
6500 ac watts / .85 inverter efficiency / 48 volts low cutoff = 159.31372549 inverter amps
159.31372549 inverter amps / .8 fuse headroom = 199.142156863 fault amps.
That means each inverter circuit should have minimum 2 awg with a 200 amp fuse.
If it were me I would use 1/0 awg and a 250 amp fuse for each inverter circuit.
Based on the above we can determine that you you battery subsystem will need to supply 318.62745098 service amps.
The details depend on the exact system topology.
318.62745098 service amps is a big deal.
What batteries are you planning for and how many?
The often overlooked fuse parameter is AIC=arc interrupt capacity.
Since LFP batteries can dump so much energy into a dead short we often suggest class-t fuses as they have a very high AIC rating.
1. WIll I need a fuse or circuit breaker between batteries before shunt?
No.
The shunt goes between the main battery negative and the rest of the system.
Orthodox design has the fuses on the positive side of the circuit.
2. What size circuit breaker or T class Fuse for this setup. I'm guessing single 600amp t fuse or 2x300amp for each bank of 48v batteries?
Depends on the batteries and topology.
3. I'm estimating 2/0 ga welding wire from batteries to bus bar is this correct?
Depends on the batteries, topology and fuse size.
4. planning to expand the system for whole home and mining once I get house built
You should consider the final form during the design phase.
The first issue I see is the BMS.
What BMS are you planning to use?
You need BMSs that can handle at least ~160 amps each.
We can figure out a topo for you after we figure out your bms solution.