You can keep Giant Gourami with smaller fish depending on the aggressiveness of the giant gourami. I just bought 12 inch (1 feet) Golden Giant Gourami 2 days ago. I put him in my 75 gallon with:
1) 2 paroon sharks (5 inch)
2) 2 upside down catfish (2 inch)
3) 1 leopard pleco (7 inch)
4) 1 moonlight gourami (4 inch)
5) 1 gold gourami (2 inch)
6) 1 dwarf pearl gourami (2 inch)
7) 2 bala sharks (4 inch)
8) 5 silver dollars (5 inch)
9) 4 archer fish (4 inch)
10) 2 black angel fish (4 inch)
11) >10 common bichir (4-7 inch)
12) 3 albino common bichir (4-6 inch)
13) 1 high fin common bichir (5 inch)
14) 1 armored bichir (6 inch)
15) 3 ornate bichir (7-9 inch)
The golden giant gourami is the largest fish in my 75 gallon. He is peaceful and gentle with other fishes. He never take a bite at other fish, even the small feeder fish. He only eat pellet.
Before I bought the golden giant gourami I observe him in a community tank in the pet shop. When I'm really sure that he is peaceful towards other fish, only then I bought him.