Learn Italian: La diretta inizia adesso. - The live broadcast starts now.

In Italian, it's very common to drop a noun and just use its describing adjective as a noun. La diretta is actually short for la trasmissione in diretta (the live transmission/broadcast). Today, it is the standard, everyday term for a live TV show, radio broadcast, or internet live stream.

Since this lesson is about "Right Dislocation" (previewing objects with pronouns), why isn't there a pronoun in this sentence?

Right dislocation relies on moving a direct or indirect object to the end of the sentence and "previewing" it with a pronoun (for example: Lo guardo adesso, il video). In our sentence, la diretta is the subject doing the action, not an object. Since there's no object, there's nothing to replace with a pronoun!

Could I use ora instead of adesso?

Yes, absolutely! Ora and adesso both mean "now" and are completely interchangeable here. Adesso can sometimes sound just a tiny bit more emphatic, but you can safely use either in everyday conversation.

Is there any difference between using iniziare and cominciare for "to start"?