In general, the settings of a sequence should match those of the primary footage type in the sequence.
Though Premiere Pro can mix footage of various types in a sequence and compensate for differences in characteristics, performance and quality are maximized when such conversions are avoided.
To determine the best sequence settings, choose a clip to create a sequence that represents the majority format of the rest of your clips. Right-click (WIN) or Ctrl-click on Mac OS on the clip and choose "New Sequence from Clip"
Please create a post in the forum if you have any trouble creating a sequence for your project.