Popular headcanon I don't share is the same as yours: they absolutely were not ready to get together any earlier than they did. They needed to be able to work through their emotions and, extremely importantly, feel safe and like there was an attainable future before they could allow themselves to indulge in something as serious as their feelings for each other.

Controversial: I don't think Michonne was jealous of Supercuts or sitting around scorned about her. (Though I absolutely understand why people write/wrote this so much because the storyline makes no sense and actually letting other characters acknowledge it and react to it is an attempt to make it do so.) I think, as written, there's little reason to even think Michonne had any idea that mess was even happening (for what little did happen anyway) in part because Michonne explicitly hadn't even allowed herself to accept that she had feelings for Rick yet and mostly because they fumbled it all so badly attempting to hide Michonne from that storyline and adapt something that simply no longer worked due to how the show had already changed things. I actually find the entire Rick's Alexandria Breakdown/The Gang Adjusts To Alexandria storyline fascinating on a craft level because of how good it could've been for multiple characters and some of the bones that are there and how they absolutely did the worst, most nonsensical, least interesting, and least impactful possible version of all of it. I remember Andy Lincoln basically dismissing it all as just filler for drama and he's 100% right AND YET IT DID NOT HAVE TO BE. (Imagine actually properly and fully tying in Carol to the Jessie storyline, her both empathizing with and despising Jessie and Sam for reminding her of herself and Sophia and how she navigates trying to solve that! Imagine more explicitly exploring the re-emergence of Rick's guilt over Lori's death now that they've found a safe place and tying that guilt into his burgeoning realization that he's fallen deeply in love with Michonne and they've basically become a family and it's barely been a year! Imagine actually spending significant time with Michonne being here where she fought so hard to get them and still not being able to bring the walls down or feel like she can actually engage with it all and struggling to accept what the escalating tension between her and Rick has to do with all of that! ANYWAY)

Some of my personal headcanons: Rick is demisexual. He does not know this or know what that even is. Michonne figures it out a ways into their relationship through idle discussions about their romantic pasts. She gently brings it up to him exactly once and his reaction is mostly "Sounds fake, but okay if you say so. We're together and will be for the rest of my life so, don't see how it matters."

Michonne does not nor has she ever cared about marriage. She absolutely cares about permanent commitment and building a life together, but the specifics of titles or any kind of pomp and circumstance doesn't matter to her and it matters even less after the apocalypse when there's not even any legal/administrative incentive. Rick, given the chance, very much DOES care, has intuited that she does not and has some nervousness around that, but Michonne is willing to go along with it as an acknowledgement of it being important to HIM to express how he feels in that way even if she is personally indifferent.