Thanks for asking!
The Silver Asphodels fill out low ranks with people who are usually desperate or easily influenced, or they just yank people off the streets. For Complicated Reasons, Na'im was stranded overseas and ended up targeted for "recruitment" at around 16 or 17 and was forced to join the group whether he liked it or not.

As far as creatures they like hunting down, Bijan (the boss) mostly just follows the money. He doesn't fuck with ghosts or djinn but pretty much anything else is fair game.
Na'im hates hunting anything sapient - at least if they're going after a monster that's attacking people, that's doing something useful (even if it's making Bijan richer). For actual trouble, Na'im has gotten his ass kicked by any werewolf he's had to fight so those jobs suck.

He HATES his lifestyle/job/life/etc. He's still with the Asphodels because Bijan has broken his spirit and he's under enough controlling magic that he can't escape.

So I think the enchantments on the mask have some flexibility - most so if I think of cooler shit, I can sub it in lmao.
The mask can carry a glamor to disguise Na'im - the disguise can be an whole ass full body illusion or just simply making the mask itself look like just a normal fabric facemask. It turns casual attention away from Na'im. Unless people are REALLY paying attention, they won't really notice him. It muffles some of the sound around him so he moves quieter. He's harder to capture on camera - he's blurry or obscured in some way. The effects can be amplified to some degree, but it takes more out of Na'im so they try to keep each effect at "just enough".

Extra: All of the Silver Asphodels have a brand or tattoo, which lets Bijan track their locations and "encourage" them to return if they're not where they're supposed to be (read: hurt them). Na'im and a few others have a worse version with varying levels of compulsion enchantments added in. The mask can amplify every effect the brand has on Na'im and ensure it works over much larger distances.

I got no measure of the blood it takes. As much as it needs is probably the easiest answer.

OOH, fun question!
So merc-naim and knight-naim have the same story up to a point
Na'im is forced into Bijan's mercenary crew and works under him for long enough that's he's mostly resigned to the work
instead of being trained to take over the crew like w/ merc-naim, Bijan foists Na'im off on another crew and that boss passes Na'im off to another crew etc etc. this happens quite a few times until Na'im is pretty far north of Dimarq, stranger in a strange land and all that, and he's doing enough work under nobility that the vibe is way more knightly than mercenary (and it's a good set-up for him to end up An Actual Knight for a Hottie Prince or Similar)

attitude-wise, knight-naim is less... flat and morose. He's still overall a serious man but he'll made a few sidelong jokes here or there. He's resigned to his life sucking ass forever and it's circled around to a weird nhilism "nothing matters" (rad) instead of "nothing matters" (kill me), so he can be more positive than merc-naim. He lets himself be more animated. He's good at Being What The Client Wants so, like w/ merc naim, he doesn't volunteer much info about himself but it's less like pulling teeth to get to know him.