Yeah unfortunately a 29gal is on the small side for Emperors. They're a bit better behaved when they are in bigger tanks where they can be kept in bigger schools. Not quite as territorial.
I don't know that I'd mix Threadfins with Barbs. I think the barbs would be too boisterous and likely nip at the threadfins. What about some Ember tetras instead? Similar overall shape and color, just much smaller and more peaceful.
You're getting awfully heavy on the bioload with both an SAE and a BNP. I'd probably pick one and go with a few Amano shrimp instead of the other.