Wr8th:
Glad you are enjoying and that your friend is considering SE to play the mod (not that there aren't enough reasons to own it anyway
).
As you said, I'd prefer a slightly different strategy than the 'Rock' for planetary defense, and force people to actually use picket lines and defensive ships a bit more.
Cpt. Kwok:
There were a few episodes that showed the defense grid around Earth, but everything was orbital, not planetary based. This can be done with sats and bases - though I do believe sat size needs to go up, as you suggested. A 'DS9' can be achieved by building a Base and arming it as you see fit.