You won't need a very large machine. Strfry is insanely efficient. I'd go for disk io over size. Notes don't use much space. You will probably end up running something even cooler like a primal instance or maybe even a search provider if you get a really fast machine (just to give it something to do).
Discussion
Hmmmmmmmmm, smart! Will do.
I5-6400? How much memory does strfry like?
It'll take as much as you give it for caching.. the thing is it's hard to tell because relays don't tend to be very busy unless you really have a huge amount of users.. for nostr21.com I have maybe 100-200 simultaneous connections and it's no where near maxing the machine out (8 gig ram, 4 vcpu vps). It's been running for months but the adoption is a slow ramp. Database on disk is only about 8 gig (running since November 2022), 3 gig when dumped to json.