Wiring an ADU

First time wiring an ADU. Here's what I want to do. Hoping someone can check my plan.

FIRST PROBLEM

1) Utility comes in at main house. ADU is currently a detached garage
2) Installing a new meter and mast on the main home per utility requirement for 125 amp
3) Have to run the power from the meter through the main homes basement and then underground to the ADU. So since this is going to be longer than 15 feet I need to have a disconnect. Well the disconnects I can find are rated 200 amp so I would have to get a fused disco and put in 125 amp fuses. PROBLEM these things are friggin expensive. What I would like to do is install a 125 amp main breaker panel at the main house. Then put in a 125 amp breaker with hold down screw. Then run power out to the ADU to another 125 amp main breaker panel. This would cost half as much.

SECOND PROBLEM

1) How to run my grounding?
2) I know the neutrals would need to float at the ADU
3) I have my UFER ground in place already
4) Install two ground rods
5) What else would I need to do for grounding.
6) water is all pex in the ADU
7) Do I need to bring water bonding from the main house to the ADU?

Sorry for the Book:thumbsup: