In the doctype fields table, each field has a default value option,
for the brand field in default enter item_hardware.brand
for the item name field enter item_hardware.item_name
In ERPNext Item price is not saved in the Item Master, it is saved in the item price list. You can have multiple prices for the same item in different price list.
For that you’ll have to call the item price list with the item code and price list, and set it to the rate.