IME, it really depends on the personality of the arowanas you're attempting to put in the community.
During my earlier years of owning arowana, I'd have difficulty with putting multiple silvers together, even though they are the less aggressive. I'd try 3, 4 and 5, but it never really worked out and had to end up selling them. I have tried on several occasions too.
I've never really put asians together...simply because I don't have the $$$. Judging from what I've seen. 5+ is definitely the way to go. There will probably be fighting/chasing though... and of course, a dominant alpha fish will form.
Currently, I have a red and a black together with absolutely zero problems. At first, when I introduced the black to the main tank, I was scared as the black is pretty much one of the rarer arowana available. I stayed up most of the night sitting on the couch just staring and waiting for the red to show some aggression. Never happened. I ended up falling asleep and woke up next morning, to see the fish were swimming happily side by side as if they were a couple. The fish were only about 10ish inches then, so they are not sexually mature. To this day they still swim together and I've never even seen any flaring.
In regards to the title of the thread, I will say try it and see if it works. If it does, great; if it doesn't, move on.