They are very messy fish and love rearranging the substrate so plants are out as they are quickly destroyed.
As you noted, a large tank (250L minimum) is needed and very good filtration. You will also have to be prepared to do frequent water changes as well.
Best to keep as much equipment as possible outside of the tank or they will break it - particularly heaterstats! An under tank heat pad would be a good consideration, or the more expensive non-glass heaterstats. You can get guards for the glass ones but oscars are good at destroying them, despite the covering.
They will eat just about anything and like variety. I know of one who loved bananas and would eat half a banana per day, along with other foods, both meat and vegetable.
Some people like to give their oscars toys to play with. A ping pong ball for instance.
Most owners say their oscars recognise them and come to meet them when they approach the tank. The one who ate bananas would continually bash his head on the end of the tank when his owner entered the room until she spoke to him, then he would happily swim off again.
They are fish with character!