Make sure you write out your entire species list before you make any purchases. Try to get species from the same ocean. The first thing you will need to do is designate your "must have" species.
Once you have made the "must have" choice, you can begin planning around that. This species will have certain light, water, waterflow requirements. Try to choose it's tankmates by selecting species that are comfortable in the same parameters.
If you do this, all will be fine. If you do not do this and you wind up with species from different oceans, or different parts of the reef, some of them may not thrive or grow...or may die.