New Mail-in-a-Box Instance

I'm about to start the journey to become my own email provider. I've got a domain and a Hetzner server going, got NextCloud up. Just discovered there's no included mailserver or installable plugin. The one NextCloud plugin called "Mail" recommends Mail-in-a-Box as a back end.

It looks good so far. They've got a setup video.
I'm no expert, but I've some experience with email DNS entries. I understand email routing well enough to fix it when other people break it.

I've been using a free email redirect service called ImprovMX to forward my domain email to my gmail, and those entries will have to come out. (If you're unaware, ImprovMX is cool, its free, and I've used it with zero issues for years.)
https://improvmx.com/

I know this is a really vague question, but if anyone has any advice pertaining to my little project, please feel free to comment.