Double checking my understanding of のことで Would just like to check my understanding of Am I correct that the nominalizes "" and is simply means 'with' for "With the talisman you have - I want to negotiate"

This is not a nominalizer. Nominalization refers to turning a verb/adjective into a noun. It looks like this:

* to eat
* **** eating
* blue
* **** blueness



is already a noun phrase, and it doesn't have to be nominalized. This means "things about..." or "matter regarding...". Please see What is the in sentences such as ?

> ****
> I want to negotiate with you **about/regarding** the insignia you have.