NVC advice

Hi there

So I have went online and paid the affidavit fee and submitted by choice of agent form (I will call and ask them to verify this on the phone today). Question is - as I must mail my documents to them, do I need to wait until I've paid all the fees etc and do it in the order they suggest on the welcome letter, or can I go ahead and send all my documents to them now to save time later?

Cheers in advance for any help!