Having one OscarFish requires a 50-or-more gallon tank, and I understand that.(Two being 75-110 and so on)
Although, my friend is keeping a great-looking OscarFish in a 40 gallon- Is that okay for the fish? Is it really a big difference, from 40 to 50, and higher/lower gallons?

Oh yeah! Is it okay to have plants with an OscarFish? Sometimes they eat it or tear at it, but what types are okay to keep with them?(I was thinking Baby Dwarf Tears, but... Theyre pretty frail, and the fish like to dig sometimes, right?)