I've got a very stupid fanfiction going. I guess it takes a lot of its inspiration from parody, maybe it's a deconstructed parody. (Characters who are out of context for their interactions but stay in-character as much as possible. They are aware that one character is a blatant self-insert who can warp reality to a limited degree.) I already have smatterings of third-person omniscience in a first-person story. (It is a really stupid fanfic and I'm treating it as a medium awareness superpower.) I've decided to start including full third-person omniscient scenes where having my self-insert there doesn't add anything and hearing it third hand lacks good detail. Or scenes where having her there would keep the other characters from criticizing the boss. I usually start chapters with condensed explanations of what happened during any time that passed between chapters, and my insert did interact during that, but then it condenses down to an action moment. I am wondering how to explain that it's going into third person omniscient because it doesn't make sense for my self-insert to be in the room. And getting into the characters' heads is what makes the most sense to me because most readers would be able to expand "he remembered being told this story" into the full details themselves. I really had fun with the first-person cross-gender-body-swap arc. (I'm pretty sure that I hadn't seen "The Prisoner of Benda" yet but it got that crazy.)
I don't know if this will help but here goes: The book Outlander (the first in the Outlander series) by Diana Gabaldon was told in first person (Claire Fraser's view point). The more recent Outlander books use third person as well as first person. When it switches to a chapter that involves Claire Fraser, the main character, she'll tell a tale from her perspective. When the story moves to a chapter about Claire's daughter and son-in-law this will be in third person. I'm pretty sure the story never went first person for a more minor character unless it was in the form of an old fashioned letter that someone else was reading. Claire's husband's letters were in first person but that's all. There are exceptions: the book Dune had clips from the Princess Irulan and I recall that they were first person but she didn't appear in the book until the end.
