5. What's the linguistic situation on this world?
Math is the language of the universe, and math is the universe, and the universe is math, and the universe speaks in math.
Seriously. There are physicists and mathematicians who claim that the universe is math. Personally, in real life, I think math is the language of the universe, but not the reality of the universe. In my stories however, it is all.
This is partially because it frightens me that the universe may not actually be a thing, but rather a mathematical probability, or collections of possibilities. The universe is real, it is a thing, we are all things that really exist in a real universe, don't we? Don't we?!
6. What's the primary means of communication?
Quantum communications is a thing in my universe and it is the primary means of long distance communication for those intelligences great enough to make use of it.
There is another means of communicating that involves alternating the universe itself. This is akin to traveling using a warp drive, similar to that found in the Star Trek universe.
This universe warping communication is so difficult, complicated and power hungry that only the most advanced of the most advanced races can use it. They, however use it at a whim. They don't care how much power it requires. It's a trifle to them.
They can and do put thoughts directly into our neuronic systems without a moment's hesitation. In fact, they can warp time as well, so that a even a moment is not a moment.
The lowly races such as ourselves communicate through electromagnetic radiation in the form of radio waves. Those a little more advanced than us have learned to keep their big mouths shut. To announce to the universe that you are a life baring planet with intelligence to exploit, abuse, enslave, destroy, crush, and subjugate is pure folly. They've learned there are races in our universe what would love nothing better than to revel in the dispiriting, disheartening and demoralization of another intelligence.