Hello,
There is no custom field that can be added automatically without limits, now if you know that there is a maximum you can define the several custom field for "outlets" AND for "outlet size" (same number as maximum).
In Custom field setting you have an option, the "Display limited to", this option allow your current Custom field to be display only IF a define Custom field, AND have the required value (in Yellow), maybe there is something to think from this.
You can process some test in order to understand, what this specific option can bring you.
Awaiting what you think about my suggestion, and if you can provide more element in order to allow us to better understand your needs, and maybe have new ideas.
Regards