Buying natural wood perches would be best! It's better for their feet in the long run. Not the straight ones you get right away from the store.

If you get a young cockatiel and they are still on a seed diet, don't try to transition them to a diet like pellets(healthier for them btw) right away. Harrisons is a good pellet brand for birds. Please note that any mixed seed with safflower and sunflower seeds have a lot of fat in them; you don't want that stuff to build up in your bird and clog their arteries or anything.

A big cage like this one will be more than plenty: Bird cage

If you get a young cockatiel, they will have the look of a female in the beginning. Its hard to tell what gender they are, so its better to wait until their 1st bday to know for sure. If you're not that patient, a DNA test at the avian vet will also do the trick. Before then, their feathers will molt when they're 6-8 months old and then their new adult feathers start coming in.

Behavior wise - they're gonna attach to you like velcro lol. Otherwise, they're very sweet and loving birds. Young baby cockatiels will make a little grunty noise when they're hungry and over time, they'll outgrow that. They're also easier to train too. They also clean themselves called preening.