It's really nice to see how you used the antler.
When finishing a custom blade I use a belt sander and progressively finer grits - maybe ending up at 600 or 800 grit then a polishing mop and compounds. It really depends upon what sort of look you're after.
Then you might like to put a patina on it afterwards using mustard/vinegar/lemon juice or you can brown or blue it.

Rab