Your VAT number will be the same as your PPS number if you are registering as a sole-trader rather than a limited company so at least you know immediately what your VAT number is. Once you send in the TR1 form the Revenue usually process it on their system pretty quickly but they are slow to write out to you and let you know you've been set up. So send in the TR1 to your local office and follow it up with a call a few days later just to confirm they've received it and ask them if everything is ok with it and if they are happy for you to start using your VAT number. There is normally no hassle with that.