First things first, I prefer to use AIM or PMs/e-mail for OOC conversation only. I don’t like to log things over instant messengers editing/formatting after the fact is maddening. I like to keep role playing in journals and have the scenes threaded. Methods for threading are entirely flexible. I know some people like to rethread the comments after every other tag to prevent collapsing or running off the page and others will string 100+ comments in one thread. I’m comfortable with either. I also come from a prompt/narrative style of role playing so I prefer to write in the third person unless there is a particular reason to use first person (the character keeps an online journal themselves or some such which I can’t see applying here). I’ll write either past or present tense depending on what the other person is more comfortable with but my default is third person past.
And if none of that bothers you; the plot I had in mind:
( Summary and explanations... )