I rather like the idea of adoptive brother m x sister f.
I rather prefer to role play a male, so I am sure that fits into your preferences.
I have just about the same motto, I give what I get, but I really do prefer to get at least two paragraphs per post from either of us. Writer's block does happen, so I do appreciate the understanding. Cursing is not a problem to me, however being an adult I do like adult/mature/explicit/(insert descriptive word here) from time to time, as long as the whole story does not become just about that. If you wanted to play more than one character in a 1x1 with me, that is fine, however I would like to continue as just being one character. I think that the idea of you wanting to play more than one in the rp is unique, and can make the rp last longer. If adult situations were to happen, would you rather fade to black and then continue said situation in a private message, then return to the thread, or just keep it all in the thread? Either works for me really, but I have no issues keeping it all in the thread. 
What age would you have the our character at? Maybe late high school, or college level, I would prefer college level, but maybe still living at home with the parents?