I would think the period 4) as defined in post #44 could be the most “happy go lucky” period for you. It could be the case for us as well.
I could not claim our kid never saw us fight (verbal only, never physical). But the fight would be very short and tamed, especially in front of the kid. Both sides know that it would affect our child and refrain from doing so. So, I think that, in our case at least, having a child could lessen the degree of fighting with each other.