I use iredmail, but I also made sure I had access to port 25 and my IP wasn't on any blacklist. This is the very first thing you should do or all your efforts could be in vain.
I would highly suggest a slight upgrade to the n305 which is an actual i series chip with double the cores of the n100 but still less than 10w power usage.
Probably true convergence between mobile and desktop, where your linux phone is powerful enough to be your only computing device. You would only need something like a lapdock (basically a laptop without the guts) and instead of a cable connecting the two, a slot maybe somewhere within the keyboard that your phone slips into. Maybe this exists already, I don't know.
The two main sources I used for initial setup was the nextcloud tuning guide and Carsten Rieger's guides which are always changing, here is the current one (in German but easy to translate).
Nextcloud is very quick IF you don't mind applying extensive PHP and web server optimizations. This takes time and may have to be redone after upgrades depending on what changes. This is why I don't really recommend it to those just looking to self host a simple file server.
The only thing that really works for smells like this are O3 (ozone) generators. You can search online and find them. Smaller ones are relatively inexpensive.
Response seems pretty reasonable to me.