Are those unmentioned crystal sabers (Descent, Gladiator, Monarch) considered dueling sabers? And if I am going to be threading into the foray of saber construction, what should I know when considering if a saber is durable enough for dueling or not?
The crystal thin necked sabers aren't duel durable because their hilts pop open in the middle and delicate struts hold it together.
Those other crystal sabers can be dueled with. The Descent's crystal is integrated into the blade plug (honestly I feel like this one is a bit of a cheat), the Gladiator's crystal is machined into the body (no moving parts), and the Monarch's crystal is exposed but the hilt remains structurally intact.
All of SF's other sabers are duel durable. That said your sabers will accrue various dings, dents, scratches, blemishes, injuries, smears, and sundry other battle scars as you duel with it. If you're considering a saber PURELY for dueling purposes I might suggest the Gladius, Reliant (w/o the control box), Arbiter, or Exhalted. The Gladius is what, arguably, made SF's reputation for crafting excellent dueling sabers and has excellent balance, the Reliant (w/o the control box) is a rugged saber that has a long uniform hilt, the Arbiter has been getting some very popular buzz recently after its' design was updated, and the Exhalted is generally considered the best dueling thin neck saber. Other options are perfectly valid but those four are what I generally hear the most positive things about for dueling.
Also w/the blades the 32" are generally considered the best for dueling as the 37" tend to be a bit too heavy for fine control.
How are you planning on constructing one?