First advice I would give you is to change your location in your profile from NZ to a more specific location so people in and around you can give you better advice.
For starting a discus tank :
Have a decent size tank to house the number of discus to intend to get.
Purchase your discus from a reputable seller preferably juvi or adult if you can afford it.
Pick discus that are active, healthy, bright in colour and eating well. Ask if the seller can put some food in to feed them. Stay away from discus that are dull looking, not interested in food or spitting the food back out and hiding in the back.
Feed them a variety of good quality food.
Maintain a good water change regime of at least 1 water change per week.
Cheers,
Ron