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.
Would be pretty tough to find an SBC with ECC at this price point.
I have seen YouTube vids in the past demoing $99 n100 mini PCs with 8GB of RAM. That would be your best bet to still have a modern low power processor in a small form factor. Also Cyber Monday is tomorrow. There's the Atomic Pi but that is only 2GB of RAM (I have one) and a dated Intel atom CPU.
IMO LattePanda makes the best x86 SBC but they're not cheap. The V1 is the cheapest and still expensive but it comes with an Arduino coprocessor so you get the benefits of exposed GPIO and µC functions. To me that's the only bonus of a SBC over a standard mini PC besides a slight size difference. It's a function that I use a lot but some people don't and those I usually try to steer away from these kind of boards.
I'd say unless you absolutely need n100 in this form factor, better to just get a mini PC.
I rarely use the manufacturer image. I'll either grab an Armbian spin or vanilla Debian aarch64 and build the device tree. I really like the layout and options on this board. If I was in the market for another SBC this would be tempting. But I also don't need video support or do anything GPU related. If you do, you may find boards like this to be lacking.
Awesome