Personally I wouldnt have more than 1 oscar in that tank, its just not big enough (you could have a maited pair, but I doubt any tank mates).
You could have an oscar and other fish if you wanted. Or one large aggressive fish. Its up to you.
I don't recommend the arowana, they get too big.
Your tank works out at 425 litres or 111 USG/95 Imperial gallons. What I would do with a tank that size is:
'Community of cichlids'
1 oscar, 1 severum and a pair of FM
For one large fish, I would either have a large male trimac/RD/midas possibly a jag (though a male may outgrow it, a female should be fine).
You could have a breeding pair of 'smaller cichlids' eg. the smaller parachromis or any cichlid around the 12" mark or smaller.
I got a 90 USG and I'm planning to breed texas cichlids, so thats another option for you.