The overhead electrical lines were not expensive.  They didn't need to be protected like underground lines would have.  It was a rat's nest, with bare wires running everywhere.  There was at least one gruesome incident where someone who touched a wire was electrocuted.  His body hung above the streets, caught in the tangled wires for hours.  Rescuers were unable to get him down for fear of being electrocuted themselves.

He was definitely bootstrapping his operation with venture capital from J.P. Morgan (one of his first customers, on Wall Street.)

Overhead was cheaper and easier although he had underground too since his system was low voltage DC but it used a lot of copper.  Nikola Tesla dug ditches for Edison for a while.

One problem is that underground New York was owned by the Astors.  Putting stuff on the surface was one thing but burying wires required paying another set of landlords!

When Westinghouse came up with alternating current, its big technical advantage was high voltage which meant longer transmission and much less copper use.  Voltage far outran undergrounding technologies.  To this day underground transmission technology lags overhead.  For example, I know of no 1,000,000 volt underground line while such voltages overhead are commonplace.

It has long been a US policy preference for cheap energy and cheap electricity.  Overhead is so much cheaper than undergrounding.

The first power cables I know about were insulated with oil filled paper made water tight with an extruded layer of lead and then protected with a wrapping of jute rope and steel bands. This is a robust technology that still is used for some cables. But it must have been expensive compared with the same ammount of copper or less in free air with some porcelean, steel and poles.

Did you realy electrifie after you built the pipelines??? Should it not have been the other way around?