I want to run power to a new barn I just put up on a piece of rural land.

I currently have an outdoor panel (Square D QO6-12L100RB) 100 amp main lug that is connected to the meter on a pole. There is not a main breaker in this panel. There are 3 circuits currently installed on it. A double pole 30A for the well, a single pole 20A utility outlet, and a single pole 30A for the RV hookup.

I want to put a 100 amp service in the barn. The distance from the pole to where the new panel location in the barn is, is 85 ft. away. I assume I need to replace the existing main lug panel on the pole with at least a 125 amp main breaker panel, and in addition to the current 3 circuits, install a double pole 100a breaker to feed the new sub panel in the barn. I would plan on re- using the existing 100amp panel for this. Is this correct?

I plan on burying 2 in. PVC to run the service wire from the new main to the sub panel. I have been told to use 2-2-2-4 AL SE wire for this. Is this correct?

Also, do I need to install an additional grounding rod for the sub panel in the barn?

Do I need to worry about the size of the meter socket if it is the appropriate size? How do I know?