RONOVE'S PROFILE

1. It was the Original King's life and the paradise in the skies (all of which he lengthened and created b/c of the demon). He'd shown it to the King and Queen and they wanted it because they were tired of all the hardship they had brought upon themselves.
2. He probably still has some of the demon power he had absorbed from eating the demon. Or, if you recall, when you first fought him, he had a lot of hard time calling up certain attacks. Perhaps he was bluffing about devouring all of Sabine's souls as he may not have known he could still do it (clearly, the Original King was super pissed, I don't think he was thinking much about it (obviously I should have given more thought to the Original King's one line, but too late!)). In any case, he was human (probably once) but since he's had the demon in him for a LONG time (thus absorbing parts of the demon), he may not be completely human any longer. And the demon part was never sealed off, it was taken out and placed into Snowe.
3. Yeah it was because he wasn't sleeping (all that much) and the demon slowly whittled away at him. When he faints after they get on the boat, the demon has control and all up to the point Snowe stabs Astra, Snowe is trying to get control back, but he is unable to because he's lost and has no energy left. When Snowe, Erio, and Dream!Astra beat up the demon in Snowe's dream, the demon has to recuperate before he can try gaining control of Snowe again (and since Erio's trapped him in a dream cycle, he has to figure out how to get out of that before he begin to whittle Snowe down again).
4. This would come up more in the sequel because you get more explanations on what demons are... but demons at their core are balls of energy. Their bodies are shields to protect themselves (a demon can exist without its body). The Original King got the demon to show him the core of energy and the Original King took the demon's ball of energy and ate it, thus absorbing the demon into himself. So it's more than just taking the powers; he took the whole demon inside himself (and Edgar and Lina took the demon out of the Original King and shoved it into Snowe so there's a different dynamic in play with those two).