I run synapse on Gentoo and it uses next to no resources except disk. Load averages 0.03 for all, 366.6MB used, 97% idle. 14 days uptime.[0] This is like rpi model B compatible.

We only have 5 users, and we use coturn on the same machine, but three of those users are also linked to glitter and matrix.org channels/rooms. The ~/synapse directory weighs in at 5GB with 2GB of that being logs.

The setup took me a 'few hours' over two nights, but my work revolves around setting up services and software[0] - it may take someone else a couple of days to correctly set up and run it.

[0] uptime reflects the rolling nature of Gentoo, and I had a certificate update at the same time, reboots are inevitable. I start with Gentoo with any new online service, since I know the pain points and failure modes. This homeserver is run on a VM in a datacenter. I have no complaints about synapse so far.