Your best bet is to get to know your new bird first and see how much you enjoy bird ownership before you think about getting more. You can learn a lot about the problems and joys of multiple birds just by hanging around message boards and reading what other people have to say.
There's no way to predict whether any two (or more) birds will get along with each other. Maybe they will and maybe they won't. Birds WILL be territorial because that's their instinct, but with a careful introduction you can sometimes avoid setting off this instinct. The surest way to avoid breeding is to have all same-sex birds, although you might still see some sexual behavior and if you have hens they might lay infertile eggs.
There's no way to predict whether any two (or more) birds will get along with each other. Maybe they will and maybe they won't. Birds WILL be territorial because that's their instinct, but with a careful introduction you can sometimes avoid setting off this instinct. The surest way to avoid breeding is to have all same-sex birds, although you might still see some sexual behavior and if you have hens they might lay infertile eggs.