First-person is harder to write than you might think. You have to put yourself into the mind's eye of the main character / narrator. You must not allow yourself to "know" anything that character doesn't know. If the character wasn't there for watch something, unless he/she was told later, no matter how important it is to the story, you can't write about it, for the character wouldn't know to talk about it.
I'm half-way into writing a story in third-person. I have a crew of 19 humans, but most of the story centers around one character, so she's in every scene. If she's not in the room, then I have selected one other character who will be. I have one such scene where she's not there but he is, written before I made this decision. Ergo, now that I have that choice, if I want two other characters to have a conversation behind her back, I have to have a reason for the secondary character to be in the room, too. Or I break my own rule.
In first-person writing, you do not have the option, which means you may have to get creative how you introduce important plot elements to the story.