currently you need to be in a guild to participate in PVP, but the guild system is a little broken- if you're not in a guild, you get no pop-up when speaking to the guild hall NPC so can't join one.
All players, old and new, are allowed, encouraged even, to host events; once the issue with the guilds is resolved, or the battle hall is reintroduced, I'll look into setting up and hosting such an event