I'd be surprised if they lured Maggie, Sr. into that position unless you also consider Harry as having been lured into being Winter Knight. I think there's likely some symmetry here with Harry's experience, and Maggie, Sr. found herself in a position where her only option out was to bargain with Mab or Lea.
Yeah, I don't think they lured Margaret into it either. My belief is she knew or was aware of the White Council's desire for a controllable star born, I doubt given her attitude towards them that she wanted their protection and what strings they might have required of her. Yet she knew the need for one, after she met Malcolm and fell in love, she felt he had the needed qualities to father a star born who could be a leader in the coming BAT. She also knew he or she would be in danger and needed protection. She also knew that Mab was very interested in a star born, but one that
she could control. I think Margaret felt that a child fathered by Malcolm would have the strength to cooperate with, but at the same time resist Mab's control. So she chose what was for her the lessor of two evils, protection of Winter over protection of the White Council, so she made her bargain.. In effect, like she found and exploited a chink in Lord Raith's armor when she threw her death curse, she found a loop hole in Fae bargaining, Mab may have thought she got what she wanted, but not really, as she has found out since Harry became her Knight.
I also suspect that Thomas was Maggie, Sr.'s first attempt at a starborn, and a super-charged WC one at that, and that any bargain with the Fae pre-dated and required/resulted in Thomas' conception. That would explain her relationship with Lord Raith, to date an unexplained and fateful/fatal pairing, as well as why Maggie, Sr. and Raith fell out (WC is also all about family, and Raith couldn't have been happy when he found out that Maggie, Sr. had manipulated him for the benefit of the Fae and for his son), and maybe also why Mab has indicated that Thomas might be offered the WK mantle should Harry no longer be the WK.
I don't think so, there is a recipe for conceiving a star born, Harry was conceived using the recipe, Thomas was not. That's confirmed by Lash in White Night that Margaret didn't decide to conceive a star child until she met and fell in love with Malcolm.
I expect a powerful-enough mortal could wear it (tho AFAIK it's un-stated that one ever has (or has not)), but it's likely more-suited to a being with more-than-mortal willpower.
So far the only mortal we've seen with that kind of will power is Harry, and he is a star born. Now the other star borns that we know of, i.e. Drakul and Listen may have that kind of will power, but they are not members of the Fae Courts as far as we know.