Desktop clients: Gossip and Lume

We mostly use web clients instead so far when on our computers, such as: primal.net, snort.social, Iris, Coracle.

On iOS, people mostly use: Damus, Plebstr, Nostur

Android: Amethyst, Onyx, also Plebstr.

With relays, I mostly would recommend you to use nostr.wine filter relay (which filters scams and spam from the public free relays) and paid relays, which you can look up at relay.exchange

In terms of hashtags #plebchain and #coffeechain are popular, with any question that you might have, use #asknostr