I didn't think for a moment that you were, i was referring more, as to how these cables would be routed from the central position to the individual plots... Which you have now cleared up, by you stating that you are following the road.... Are you running this buried cable in ducting, or just direct buried??
Don't be tempted to run 2 core SWA rather than 3 core, using the Armour as the earth, it won't comply with main bonding requirements. To cut costs and reduce cable size, consider using 2 smaller cables in parallel. Direct cable burial over a 150m is going to need a lot of man hours to remove sharp stones and other debris from the cable trench floor and sifting of excavated soil for the first backfill layer after the soft sand. It could well turn out cheaper to duct the cable, which if planned correctly, could provide a means of replacing the cable(s) in the future, should it be deemed necessary....
Oh and if i were you, i'd get everything in writing from this Electrical Engineer you talk about. Is he the guy that produced the cable size print out you posted, because there are a few fundamental data errors on that calculation sheet??