I have tried hosting a Tor relay on a VPS in the past and it was bottlenecked by the CPU at barely 20MB/s, although to be fair this was without hardware AES. More importantly for you, the server’s IP started getting DDoSed constantly and a whole bunch of big internet services just immediately blocked the address (the list of relay IPs is public and many things just block every address on that list instead of only exit nodes). So any of your machines are probably at least somewhat up to the task (ideally if they have hardware AES support), but this is definitely not something I’d do on my home network.
I have tried hosting a Tor relay on a VPS in the past and it was bottlenecked by the CPU at barely 20MB/s, although to be fair this was without hardware AES. More importantly for you, the server’s IP started getting DDoSed constantly and a whole bunch of big internet services just immediately blocked the address (the list of relay IPs is public and many things just block every address on that list instead of only exit nodes). So any of your machines are probably at least somewhat up to the task (ideally if they have hardware AES support), but this is definitely not something I’d do on my home network.