how many do you want?
Me and nostr:nprofile1qydhwumn8ghj7emvv4shxmmwv96x7u3wv3jhvtmjv4kxz7gqyzrpssgfat5n0kxklxqtfg95dkjw7rvc86k7gqlwrdxqk677yw95w6r70u3 did load testing against a bunch of different relay implementations, and so far strfry is in the lead with the ability to support 40k concurrent "users" (according to our K6 test criteria) on a single node.
The only downside of strfry is that the database and relay server have to be tied to one machine, so it cannot be scaled horizontally without replicating all of the data across each node.
Our K6 setup is here: https://gitlab.com/soapbox-pub/otherstuff-relay-k6
Discussion
if "a lot", you'll want a cluster of instances: haproxy on the domain address dispatching to a pool of read-only instances that pass writes to a single instance that's not exposed. the write instance then propagates updates to a hot spare and back to the other instances in batches