I Have dwarf puffers and amazon puffers. Amazon are much more docile and a bit bigger plus better in groups.
My dwarf puffers were fine, my buddies were jerks. Ive housed mine with other fish fine and had both in a 5 gallon planted together. Im currently moving my surviving dwarf to my 55 with my amazons because the new betta he shares with is a jerk and harrasses him.
I have never seen my puffers go after larger snails. I have had mystery and nerites with no issue. I have also had shrimp with them. For the most part these fish are pretty smart and wont go after something they cant outright eat. I have seen my dwarfs eating a DEAD ghost shrimp but it was already dead so who knows. if you have a 29 you will be fine with Id say 3 dwarfs. They will leave the khulis alone for the most part, but again EVERY puffer is way different in my experiance and its always a crapshoot.
The line of site bit is true as for almost all fish. I believe my 5 gallon pea puffer tank is in my gallery if you want to see it and they have been in there happy for a couple years. Its a shame I lost one but after a water change I forgot to plug back in my heater and one got VERY stressed and sick. I was devastated honestly because when you interact with these fish and see how intelligent they really are its hard not to feel bad. My amazons will come right to the tank, eat from my hand and are great to watch. When I had them in my 29 they did nothing but glass surf all day. Also the amazon puffers are a pain because they need their teeth trimmed. In fact Im VERY late on that and actually noticed algae growing on one of their teeth!
If you have specific questions let me know, but again everyone who has had these fish probably have different experiances.