" Entering the atmosphere already above 10,000 (half of the mass of the atmosphere) would decrease structural loading. A high energy laser could also super heat the flight path just before to lesson resistance (like lightning splitting the air). "
Quite early in the discussion, you described an elegant suggestion. I have only two things to recommend to make it even more useful.
First, I would not make it an equatorial mountain. I know the reasoning behind this, to take advantage of Earth's rotation. But I would place the rail gun in Antarctica. The cladding necessary to prevent damage to the ship -- the ablative material which would protect it, would be ice. Maybe even a lot of ice.
The idea about using a laser to heat the air ahead of the vessel is also a good one. That is why I used it in a Science Fiction novel published last year. "...high output laser energy is sent forward to prepare the undisturbed atmosphere in front of the ship to expand and get out of the way, so we can slip through without pushing the air..." (page 189, Chapter Sixteen)
My second reason for locating in Antarctica is a commercial one. Once the ramp is set up to launch "packages" (electro-magnetically) toward the edge of the atmosphere, one could contract with governments or individuals in desert areas of Australia or Northern Africa, or any desert on Earth, to deliver fresh water on a contractual basis for irrigation purposes. This should pay for the overall enterprise, and allow up to five million square miles of desert to become productive agricultural zones.
Better plan on building up the new gravel pad at NO a couple more inches to compensate for the extra rise of sea level.