Looking at hardware I have lying around and thinking this Pondesk unit with a Intel Atom CPU E3845 CPU is certain a low powered unit.
Would you expect with pfsense 23.01 installed, probably 50 devices and OpenVPN running it’ll be quick enough. I do hope to add and learn Snort in due course.
Currently I have a Dell R220 in the loft rack, which is probably using 20-25w and idle most of the time.
Virgin Media 200Mb connection, sadly no 1Gb in my area yet.