i will link this here:
Major theories comes from this great discussion, have a look in there and build your own also :)
regarding your question:
*2 There are many thesis on that, so i cannot give a good answer, look at the link for more. In anycases if we want look at the facts we can state that's is a refers (in a misterius way) to the Great Ones. Why? Because you can see pale blood when you slice them. Need further investigation/Thesis building.
*3 So it seems. There are major thesis in this argument also, but most of them assume that the event you are fallen into are placed into an another plane of existance. A "Nightmare" that is a specular copy of the reality, where you are not able to wake up. You will notice that with the 1° ending and the "True" ending. Another proof of that is the "hunters" slayns do not respawn as you die.
*4 Into the real world the Hunt is an event that periodically (it's not stated if it has a fixed occurence) as soon as there are too many beasts around. Into the "Nightmare" realm, the hunt is perpetual.
*5 Major thesis in here too. But we can assume that the cause of the plague is from Ludwig himself, who found "something" into the deeps of the labyrinth.
*6 Blood. To much greediness for blood.
*7 Well the science was monopolized by the church, so the religion could say the fuck they prefer to the population. Eventually the fear of the unknowledge Great One, builds up rites (mostly factually useless) and prays to hold back this fear. There are no proof of "actual religionous power", there is no magic at all, the only stuff "magic-alike" is through the use of spectre, which are actualy corposes or extention of grater being, or actualy pieces of "human-no-more".