Is Galaxy Apps a legimate App? (kitkat, samsung galaxy app 3)
Galaxy Apps is the new name of Samsung Apps.

Samsung Billing is also legit, as per Informer answer:


  The application is used to purchase apps through Samsung Store
  application that is delivered with Samsung phones. Samsung Billing
  acts as bridge between Samsung Store and payment servers. Without it,
  you will not be able to purchase anything. It's safe to be removed
  because it can be installed at a later date in case you actually need
  it.