Some questions and comments on my experience.

My main motivation to switch was that emby seemed to be buggy on the client side, keeping track of what episode of what tv show and season I was on. I'm hoping jellyfin helps with that.

On the server side, I wanted to keep both servers running. But there were port conflicts. It was difficult for me to find in the Jellyfin docs the right config file to set the ports. So I ended up changing the emby ports. (Since I could find the emby config files.)

diff /var/lib/emby/config/system.xml.orig /var/lib/emby/config/system.xml 
9,12c9,12
<   8096
<   8920
<   8096
<   8920
***
>   18096
>   18920
>   18096
>   18920