I have the 'default home page' set to custom lightning page that I set using the lightning app builder. Yet my developer org loads onto the setup home. How can I make this org load on the actual home tab?
This is a per-user setting each user can configure to their liking. Go to My Setup, Display & Layout, Customize My Pages. There, you can select the default tab to see when you log in, and check a box to change your default landing page to Setup. Uncheck the box and save your change, and when you next log in, you'll land on your preferred landing tab.