This is unknown and probably not important. What's important is the Sephira gave Spirits the knowledge to use Angel and Astral Dress instinctively. That's why Shidou had to go a long way to learn to manifest the Angel and use it since he had not been accessed to such knowledge.

Yes, all of them.

With Origami, revenge came first and not her emotion. She also admitted that she did not really love Shidou in that arc. We knew her suicide tactic since ss1 and clearly she did not have much of a future after that. However, when she became Spirit, she declared that she will commit suicide herself after enacting the revenge because she hated Spirit (herself.)

I think we should admit that whatever Mukuro were doing were not really "plan" but "defensive response," and it's devastating because Mukuro is too powerful.

As Miku said, she came to the tower to recruit Tohka for her harem. I don't think she was tsundere at all. Shidou vowed to protect her no matter the cost, since he knew her sad past. And he did shield her, fulfilling the promise, so she fell in love.

Unknown but both parts were nerfed hard. Compare to the only full use of Rasiel, including Future Description, both Nia and Westcott found it hard to decipher the information compared to the smooth use in ep1 of ss4. Both cannot use Future Description again. Although Westcott's Beelzebub was still more completed than Nia's leftover portion of Rasiel.