ok...my 2 cents worth.
the transformer is way too far from the house. Im an electrical contractor, and we shy away from ever putting the transformer that far. You will have to size up the secondary wires to such a large size, that it will be cheaper to have them run their small primary wires further.
Second....im not sure what kind of soil you have, but a mini excavator will definitely outperform a ditch witch if there is any rock at all. I can place 200-250 feet of trench an hour using the one i rent for work.
If you ever plan on adding shops, wells, etc. I generally bring in 400 amp service to a point 1/2 way between the intended buildings and then place a 400 amp meter main, that contains two (2) 200 amp breakers and a small 30 space electrical panel. The small panel works great for landscape, wells,etc. The 200 amp services work great for house and shops.
just a note here - using Southwire's voltage drop calculator
if you require a 3% voltage drop (the smallest recommended ) and want 400 amps, 250 feet away. The minimum aluminum feeder size would calc out at parallel runs of 500 MCM wire, which equates to aprox 4 runs of 500 mcm @ $ 1.48/foot plus 2 runs of 350 MCM wire @ $1.15 per foot plus 2 ground wire runs for a cost of $9.22 per foot of secondary plus conduit plus labor (this is for 400 amps). for 200 amps it would be 1/2 of this.
if you would be willing to accept a 5% voltage drop, you could get away with even a cheaper cost, but risk dimming lights, and other nasies in the future.
if you placed the transformer say 50 feet from the buildings, and placed a 400 amp meter section say 10 feet from the transformer, you could get by with feeding the 400 amp section with single 350 MSM wires and each of the 200 amp services with 4/0 alum (aprox $0.50 / foot x 3 wires ). This usually works out the cheapest route in the long run.
