First off, you have to make your own topic for your specific contract with a superstar/Diva. They can all be in the same topic, and you don't have to say make a topic for a Christian contract, and a separate one for your other superstar or diva. If you switch, however, then yeah you have to make a contract for that new superstar you hold up.
This is rather simple. Remember to read over the rules before joining, and look over the free agents on the Roster section for available superstars and divas. You may take up to two superstars along with a diva making it a total of 3 playable characters for one person. Keep in mind that you can also just pick one person, or two. Just choose whatever suits you best. Here's the basic template for a contract.
*Superstar/Diva Name*
*Alignment ( Heel or Face )*
* Available Schedule*
* PSN ID*
Here's my own to make it more easier for everyone.
Superstar Name: Christian
Alignment: Face
Schedule: Every day, whenever I am on PSN
PSN ID: Mark_Death
Afterwards you just need either mine, or the Co-owner's approval and you're set. Just because you make a contract doesn't mean you are bound to that specific person. You can always switch if you're not finding any compatibility with a chosen superstars/Diva or just drop them all together.