Hello - on the inventory item / warehouses, we have many many unused fields, how do I start removing these? i dont see them under customize form. Thank you!

That's not customizable unless the Advanced Item Location Configuration feature is turned on (with its pros and cons)

Be warned that once you turn on the feature Luis mentions, I do not believe you can turn it off. Additionally, those fields are not customizable on the form as they drive the supply planning functions and are scripted onto the item-location record here.

You can create your own search and use it as a sublist on the item record.