It's fair (I think) to argue that the The Line (as it seems to have become called) is, perhaps, one of the first MegaStructures to be built here on Planet Terra. Obviously, things like the assorted, huge pyramids may fall into this. Even the large skyscrapers.
The Line is (functionally) an arcology that is being built sideways along the ground rather pointing up into the sky.
I view planets with a very high Hydrographic Percentage of 9 or A to have much of the land being mountainous in nature, basically mountain tops showing about the water. That does limit the amount of arable land to produce crops. Tunneling with hydroponics and artificial light seems more reasonable. I would not regard them as worlds capable of supporting a high population, maxing out in the millions, or Population 6.
But you could also have a New Zealand, Hawaii Islands or many other Volcanic Island chains also. An Arcology would free up more arable land for crops on them. I would guess how best to use what little land you have would also be determined by the world's TL.
You are very likely correct, as that is what I assume. Genetically modified kelp would figure prominently on the menu. On some of the planets in my sector that I am building, you might also find Stellar Sea Cows, seeded by the Krell.
Not as such, but it an idea.
Yep.
On small planets with thin atmospheres, though I tend to go down rather than up.
