The Asian arowana species name is Scleropages formosus. Remember that Asian arowana's are illegal to own within the united states so if you are US based you wont be able to buy one.
The Black ghost knife and armoured bichir are too small to house with the other tankmates, at some point they will get eaten.
If you are buying 2 rays make sure they are both female, if you end up with a male/female pair the male could overly harrass the female to the point where she becomes ill or dies. Mixed sex groups are better in 2 female 1 male ratios.
Leopoldis are now illegal to import from the wild so if you are keeping these you should make an effort to breed them, when the captive bred stocks run out there will be no more.
If you are buying a tigrinus buy the biggest one you can find and afford (remember that a 4" fish is likely to cost 300 dollars/pounds), small tigrinus under a foot long are very sensative and die very easily, larger specimins are a bit more stable.