I think I can answer some of your questions, just based on my own experience and nothing else:

1) First of all, RP realms are not well enforced in regards to RP rules. There IS RP, but usually it's isolated. For instance, most RP will not be seen by someone popping into the realm for the first time and walking around a city. Generally you have to take initiative to find rp...Which would mean finding the rp community (which is thriving on our realm, generally in guilds and guild-related events but not often out-in-the-open world RP) This being said, when even the basic naming rules are not enforced, you're not going to get kicked out of the realm for not Roleplaying. In fact, the majority of people on RP realms are NOT roleplayers.

2) In Roleplay, the general rule is that everything in 'SAY' is roleplay. Now obviously, when most of the realm are not rpers, this isn't going to be followed most of the time. But when you're at an rp event (such as a story night or tavern gathering) where it's a controlled RP environment, RP is 'SAY' and anything that is out of character (ooc) is said in ((double parenthesis)). In my experience all RP is in text form.

3) Our guild has a specific OOC (out of character) channel to speak from. There's a big difference and separation between the character and the person.

4) As for big runs of dungeons? I can't say I know much about this myself, as our guild is a heavy rp guild and while we do do dungeons and whatnot, we don't do much PvE content. Occasionally we'll run a dungeon or even be doing quests and to have fun we'll RP in 'SAY' and emotes as our characters, but in Party chat we'll be OOC. So pretty much everything that goes on in a regular guild CAN and WILL happen in an RP guild that wants to do instances but with the added spice of rp to enhance the immersion into the world.

As for vent, that's generally OOC chat...RPing is like writing a novel but you only control one character. That's the exciting part about it for me.

I suggest checking out rpmadesimple.com as it's a really great resource for new rpers or simply people interested in learning more about rp.

If any other experienced RPers want to chime in please do. This is simply my take on these questions and I'm sure there are a variety of experiences that are completely different than mine :)