Right-o, gun kata it is.
As for the shadow hand damage delay, I don't see why not since you're just delaying your on-hit effects and not stacking them. But then I'm also inclined to let maneuvers work with ordinary and syrneth firearms too.
Hm. Book 2 also introduces combi-weapons that act as both melee and ranged weapons. That could be an interesting way to mix maneuvers/kata with their off-type weapons. If the DM is willing to flex a bit.
Frankly, comparing this stuff to magic, I have very few compunctions about being generous with interpretations. You're paying more xp for a more limited special effect that's almost impossible to leverage outside of combat. Although, still, overall its safer in the long run than dancing with the warp tables.
I mean, a 50m base range knife throw is nice, as is a quad opportunity attack, or punching someone for five rounds and on round six all their bones break. Those are all nice. They still ain't 40m almost at-will teleporting with a laz cannon tucked under your arm, or summoning a 8k4 in any skill spirit/critter to do your bidding. So I tend towards being generous in my interpretations here.
Plus I can always slap a few sword schools on a monster and build it a fun signature move because monsters don't pay xp. The players like those too, fun monsters.