How many weeks before the wedding do registrars make contact to finalise the ceremony?

I think it varies from registrar to registrar so probably best to call and ask yours.

i think ours is about 12 weeks before which is also when they need to be paid.

As soon as we went to give notice, we got a 'your ceremony' pack from the registry office (we gave notice somewhere different from where we're getting married). There was loads of information about the ceremony and we've been sent a ceremony planning for asking us to confirm all the details like wording, vows, witnesses, who'll present the rings etc. We've been asked to send it back at least 4 weeks before the ceremony.

I imagine they'll contact us to confirm everything when the final balance is paid 12 weeks before the wedding.