So I'm doing this calculation as I write this comment so I'm commited regardless of the outcome.

• The sun is (roughly) 2 x 10^30 kg
• The sun makes up 99.86% of the solar systems mass
• That leaves about 2.8 x 10^27kg of mass in the planets and asteroids.
• Earth weighs about 3000kg/m^3 at the surface
• I'm going to assume the shells are about 1km thick, or maybe 500m but with an extra 500m worth of stuff in a more condensed form as structural support.
• So 1km of surface requires 1km^3 of material or 3 x 10^12 kg of material.

Assuming we can get all of the solar systems material and use nuclear fusion to turn all of the gas into heavier elements (I assume anyone dismantling solar systems has workd out fusion) that results in about 9.3 x 10^14 square km of living space. about 1.83 million earths.

The total surface area of the solar system (with rough guesses for the size of the rocky cores of the gas giants is about 9.8 x 10^9 square km.

Since we can't really detect small planets in other solar systems I'm going to assume they all have roughly the same amount of planet as our own one. So all in all we get just under 100,000 solar systems worth of living surface.

Ok so its actually about 0.1% of the milky way in terms of living space at best. But thats still pretty damn good and its all withing fairly managable lightspeed communication range of just a few minutes delay at worst. And we could get to 100x that if we could do starlifting and removed just 14% of the suns mass.