I mostly speak from my experience on Chaos and some occasional RP on Light.
There's both adventure and social RP. There are a lot of people who usually do both, at least on the server I'm on. While there are public events that are not social, adventuring events are usually mostly within FCs, while people visit RP venues (which
DO NOT take
actual Gil, mind you) when not doing events to meet other characters, hook up IC, find work, or even get recruited into an FC. They can range from taverns to fighting arenas to ... more adult oriented venues.
The rolling system usually varies from FC to FC. Some require character sheets, while others are very simple and just need you to reach a certain threshold on the dice or are just freeform to begin with.
Some FCs have weeekly events, some make events that based on character arcs or a FC wide event, like getting a job overseas in... Thavnair or Tural.If you are already part of a non-RP FC, you can just join the Discord, and whether you are an In-Character member or an associate is usually up to you.
To address the elefant in the room, ERP does happen, but it's usually part of the character's arc or the character visits an adult venue IC. You do not have to play it out, you can Fade To Black and timeskip to after the do was done. Sex is viewed as part of the RP but not required.
[EDIT]
I forgot to provide the actual resources to get into RP:
https://www.thekweh.com/rp-guide
https://ffxiv-roleplayers.com/topic/...play-handbook/