Hello @shinyobjects ,
The flat rates can be configured from Shopify settings-->Shipping and delivery-->Manage rates-->add rates--> set up your own rates. Maybe reading this article from Shopify will help you better understand how to configure flat rates.
You can add the UPS account from the same Shipping and delivery tab itself. At the bottom of the page, there is a section for accounts and integrations--> manage integrations-->connect carrier account
Check out this article as well!