I'd agree: if you're going to do multiple first person narrators, it's best to only switch at chapter breaks. I see this done a lot in YA novels, and the chapter is usually preceded by the name of the character, which makes it easy to keep track of whose head you're in. But I'd also agree that if you're going to take this approach it's really important to give each character a distinct voice. I've read way too many novels where the different first person voices just blurred together, leaving me to wonder why they did it like that in the first place.
Admittedly, I am not a fan of multiple first person POVs at all--I've seen it done well a few times, but for the most part it feels unnecessary to me. If I'm going to be using multiple POVs I generally just do a close third person, limiting myself to one POV per scene or chapter break. I use first person only when I'm spending the entire novel in one character's head.
I think the reason for this is that, when I'm reading third person (even a close third person) it's the narrator telling the story--and the narrator can do anything, so it feels totally natural for the thoughts of multiple characters to be explored. But in a first person narration, I feel like it's the character telling me their own story in their own voice. It's an inherently more intimate and personal style, like I'm listening directly to someone talk. But if the story has numerous first person narrators and is constantly jumping from head to head, it breaks that illusion and creates a kind of cognitive dissonance. It's like I'm in a roomful of people who are all talking over each other, trying to tell their own stories. I can handle switching back and forth between two first person narrators, anything more than that quickly becomes too much.
Just my personal preference though.