Angelfish are schooling, and need to be kept in numbers of 4 or 5 as a minimum. Unless you get a mated pair, then you could have two. They would have to be acquired as a mated pair, you can not expect to just add a male or female and expect them to pair up. If getting a school, they should all be acquired at the same time to reduce aggression.
For 4-5 Angels you would need a 55 gallon aquarium.
Their natural environment consists of lots of tree branches/roots with a floating cover of plants, dimly lit, and possibly some Sword plants.