It's good to see that Starhawk is continuing with this story despite his other distractions. In this latest episode, I like the emphasis on the sheer scale of Icaran achievement, and the foreshadowing of a titanic conflict in the near future.
A few nitpicks:
Admirals usually don't take over a ship's bridge and give orders directly to the helm. They issue general instructions to their captains and let them give the detailed orders to carry out their assignments. Of course Admiral Ross may have taken direct control just for the fun of running a ship again.
"Two thousand square kilometers" isn't a radius, it's an area. A circle with an area of 2000 km^2 has a radius of just over 25 km.
Our sun contains about 99.85% of all the mass in our solar system. To build a sphereworld with the mass of our sun, the builders would have to import the mass of about a thousand Jupiter-sized worlds. Not to worry, though. Freeman Dyson estimated that a sphere 3 m thick could be built around our sun at a distance of 1 AU using all the mass of the planets and other "debris", or several cm thick using only elements with atomic number greater than 2.
When I looked up Dyson spheres I was surprised to learn that Dyson's original vision wasn't for a solid shell, but rather for orbiting stations in such numbers that they intercepted all of the local sun's output. Although SE IV uses the term "sphereworld", authors can interpret that concept in various ways to suit their stories.
References:
http://www.nada.kth.se/~asa/dysonFAQ.html
http://en.wikipedia.org/wiki/Dyson_sphere