1) Do Bound Armor sets still give a bonus?
2) Can you miss-match Non Bound and Bound items to form an armor set?
3) Can you make duals out of Bound items?
1.) As far as I know only R grade and up.
2.) R grade set can be mixed with Bound, Normal and Blessed items, as long as the name and the type (ie.: Twilight - Robe - Restoration) is the same, then it's considered a set.
3.) I've seen bound duals on blacksmith NPCs, however not sure if there's any restriction and if Mammon can make higher grade duals.
1) Do Bound Armor sets still give a bonus?
2) Can you miss-match Non Bound and Bound items to form an armor set?
3) Can you make duals out of Bound items?
To answer your 3rd question, yes you can make bound duels at the blacksmith up in Gracia.
I get the set bonuses for all grades of Bound items so I dunno what are you talking about. What was the point for NC to add Plated leather set (example) as C light in the Path of awakening. If there were no set bonuses you can just go for the higher P def lol - Theca or Drake...