Maoyuu Maou Yuusha/WMG

Several of the technologies and ideas the Demon Queen has originate from our world

 * I'm not sure what you mean by this WMG. For starters, do you mean that these measures have been implemented here or do you mean something like... she used her magic and research to find out about ideas and such from a world like ours?
 * The latter.
 * Some of her phrasing does seem to support that proposition, though it's never explicit that I've noticed. But she's talked about how worlds have been destroyed in the past ("Don't think about that too much," she tells Hero), and if she knows about earlier, destroyed worlds, she may know their technologies as well ... or techniques from worlds that weren't destroyed.
 * She was preparing to introduce gunpowder weapons ... but one of the human factions linked to the Church hierarchy got hold of the design. As shown in the Comp Ace manga, these are muskets, looking more like flintlocks than any of the intermediate steps in firearms development: matchlocks, wheel locks, etc. They're starting with flintlocks. This argues for imported technology rather than simple innovation.

Young Merchant and Grand Princess Fire Dragon
End up becoming a couple, because Pair the Spares.
 * The Comp Ace manga seems to confirm this. She sent him to "battle" her father; apparently, victory was a condition for winning her. He negotiated rather than fighting, and Archduke Fire Dragon cheerfully declared himself defeated.

Lone Winter King and Big Sister Maid
Become a couple, because Pair the Spares and she's brave, intelligent, and inspiring -- remember she not only roused the crowd to throw off the Church's mental shackles, but stirred the young King to personally defend her against the Church executioner. Sure, it's normal for royalty to marry royalty, but that can lead to becoming inbred and effete; choosing a sturdy commoner as his bride would add vitality to the royal bloodline. That he did defend her might help incline her to be amenable to his courtship, too.