Which to choose

1) I would go with the +Def -Spd Hector, as taking a Res bane will hurt his ability to tank mages, and his attack is already good as is.
2) I would keep the Brave Bow+ because a guaranteed quad is better than desperation, as you already make two consecutive attacks with the Brave Bow.
3) I don't believe the merge matters, but I honestly don't know too much about it.
4) I would go with the neutral IV Flora, for the same reason you said; she can still tank DC users with her weapon. Also, that DC tanking is kind of niche, but mage killing is far more common, and a Res bane would hurt that, so go neutral.