Ask HN: Im starting a BETA, what needs to happen in preperation?

I'm kicking off a public closed beta for my website https://www.filmitright.co.uk, the first of a couple I'm planning over the next six months. Feel free to sign up and check it out. My questions are: Do you need a large volume of people to make the BETA test successful? Is there anything that needs to happen either before I start it or during?