I am in the process of building a new addition and attached garage.

I currently have 200 amp service 4/0 alum. 100 feet UG from house to (my) pole in 2" conduit. It then crosses the street to utility owned pole, approximately 125 feet OH. (dashed yellow line)

I would like to remove the existing pole as it impacts the relocated driveway. I would either replace entrance wire to a utility owned pole on the property line (left side of picture) or extend the exsiting 4/0 alum to this pole. I perfer the latter so I don't have to tear up my lawn, plantings, driveway and I will not need as much wire. Can I splice 4/0 alum underground? (green line). The new wire would be 225 feet UG to the pole on my side of the street and approximately an additional 125 feet acoss the street to the pole with the transformer. Is this too far? What is the max distance for 4/0 alum?

Should I consider installing a new main panel in the garage (red line) and use my old service panel in the house
As a subpanel? This may make sense as I will be removing the old detached garage and the wire from the house-garage and garage-barn.

Can I splice into the exisitng wire leading from the house to the garge and reroute it over to the barn.

Sorry if this was long winded

I like the idea with the red line.

Have you contacted the utility company about your proposed plan? They may have something to say about this as each utility has their own requirements.

Splicing underground wires is always a challenge, esp if the splices will be buried. If this needs to be spliced, and yes it is possible, I would use a handhole at the splices so that they are always accessible and can be better protected.

Sizing this feeder will depend on the utility, if they own it or if you own it, and the connected load. The calcs I did based upon a fully loaded 200 amp service, assuming the max of 80%, shows that 250 MCM aluminum wire is needed.