Talk about timing! You have no idea.
I have been craving a brother/sister RP.
The RP you describe is one of my absolute favorites, especially if the brother is older by, say 5 or more years, so there's always been some hero worship on her part and protective instinct on his part. I'm willing to negotiate on the age difference, however. Another thing I usually like to include in this RP is the brother's many failed relationships, caused by his unacknowledged desire for his sister. No woman can ever hold his attention long because he compares them all to his sister. At the same time, the sister has had relatively few relationships (which always fizzle out) because she's never met a man who could really get her going since she always compares them to her brother. Because of that, there can be a sexual awakening now that she has the man she wanted all along.
Submission is a given. I'm fine with the initial non-con as long as it's just reluctance because it's her brother, not rape, and once she gives in he should lighten up.
Anal... it's not a must-have in my RPs but it's fine as long as it's not non-con. How about him being heavily into anal while she's never tried it, so he teaches her and she becomes more and more enthusiastic about it as the RP progresses?
Light bondage is fine.
Long-term is perfect. I prefer to take time to flesh out the characters, establish backstory and build sexual tension. I can post at least once a day, as a rule; what do you consider "often"? Sometimes I'll be able to post more than once a day; it depends on who's doing what in my household on a particular day and what times of day you're posting. I've been told I'm a good writer; in any case, I like to write. Whatever number of high-quality paragraphs you want per post, I can provide.
Last but not least, I am female OOC.
Let me know if you can work with my ideas.