How can I change the sort order of products globally, using a custom field, and option

I would like to change the sort order of products globally, using a custom field which I would populate externally and then import into Shopify.

Then in the Collection default Sort Order drop down Menu, I would like to create an additional Option ( labeled for this posting “Custom”) , which is also selected by default , and on selection displays the products using the values entered into the custom field.

Questions :

Is there an existing solution ? , or if not..

How do I create the custom Product field in Shopify ?

How do I create the new default option “Default” in the Collection drop down sort list

How do I then ensure that products are displayed in the required NEW sort Order “Custom”

The values of the new product field would be AlphaNumeric based on our existing data, and the expectation is that products would be sorted from left to right based on the value, eg

Product Custom Sort Value Listing Order

Blue AB123 1

Red JD001 2

Yellow JD005 3