Okay yeah I gotcha! Regarding the RP section, I understand wanting to make sure you are committed first. One ting ya could do though is post on some on some of the threads or join the skype chat that we have. You would be able to meet some of the people in the section and get a better feel for it :)
As for other sections you can peruse, I would say definitely take a look around the off-topic discussion sections. The Mall, Treehous and Playground are all places that are a good way to just post some fun stuff and become a bit better known. PokeTrivia is very similar to that. Just nonsensical fun lol
Yeah I understand the ROM Hack stuff, that's usually all I say too when I decide to go there and post something lol
Lastly, Onederground, as i understand it, is in reference to the one year anniversary of the UnderGround section of the forum. It's in the Off-topic discussion portion and involves a bunch of mafia/murder games essentially from what I've seen. So I think this is just a way to celebrate that section and all the regulars have that signature.
If you want to know more about that section, I'd be happy to point you towards some of the regulars that I know frequent the section!