Best Way - Copy a record a number of times

 So here are my two approaches.

The simplest way is to set up an automation which will create, sa6, 20 child records. The automation would be triggered by a child record being created and a summary look up from the parent telling the child record that it in fact was the lucky one which was the first child.

The automation would create say 20 children each numbered from 2 to 20 respectively. Then the last step of the Automation would  delete any children where is their assigned child number was greater than the number of children called for on the parent record.

It doesn't sound like you would need more than  20 or 30 based on your pizza example.

But if you did want to generalize this to a higher number. I have done automations in the past where the automation creates a record and then updates a counter to the previous value of the counter plus one. And then the last step of the automation triggers that same automation to run again. That is to say it is possible to make a looping automation that calls itself. You just have to make sure that you don't create an infinite loop and there is a condition where the automation knows when to stop running.

 But my first suggestion is simpler to set up. Just create a fixed number of records and then the last step of the automation will delete all the extra ones that you didn't need.