1. I recommended using 1.19.2 since the latest version isn't entirely stable, though you can connect with any version 1.14+
2. This doesn't really make sense since Fabric is a modding API and Spigot is for plugins, but the specific API they use shouldn't matter to normal players. You don't need a special client to connect, if that was your question.
3. play.roleplayhub.net
4. Just log in to the server, create your character, and go find some people to roleplay with. There's no real formal process to it, just put yourself out there and meet people.