Can I set all VAT to zero as a default as I'm not VAT registered?

Hi there, @garlandsfarmeque.

Yes, you also choose the option No VAT when creating transaction.  I'll show you how to do that. The sample transaction I'm going to use in this method is for invoicing.

1. Go to the + New and select Invoice.
2. Enter the necessary details.
3. Choose No VAT after selecting the drop-down button in the Amounts are field located above the Amount column.
4. Verify the details, once done select Save and close.

I've also added a screenshot for your additional reference.

You're always welcome to post in the comment section below if  you need further assistance or questions. I'd be glad to lend a helping hand. Have a beautiful day.