I manage several Garage clusters and will keep maintaining the software to keep these clusters running. But concerning the "low level of activity in the git repo": we originally built Garage for some specific needs, and it fits these needs quite well in its current form. So I'd argue that "low activity" doesn't mean it's not reliable, in fact it's the contrary: low activity means that it works well for us and there isn't a need to change anything.
Of course implementing new features is another deal, I personally have only limited time to spend on implementing features that I don't need myself. But we would always welcome outside contributions of new features from people with specific needs.
You also want fast networking, I just use 10Gbps. My nodes each are 6 rust and 1 NVMe drive each, 5 nodes. I colocate my MONs and MDS daemons with my OSDs, each node has 64GB of RAM and I use around 40GB.
Usage is RDB for a three node OpenStack cluster, and CephFS. I have about 424TiB between rust and NVMe raw.
Smr drives are absolutly shit-tier choice in terms of drives.