In case no one has answered your question at the beginning of this: The original series followed the Manga until it caught up, and then went off on its' own and didn't follow the manga at all at the halfway point.
Brotherhood doesn't assume you've watched the original, but in case you did, it kind of shortens the early stuff from the manga over the first several episodes and then follows it to the end.
So you do not have to watch the original series ever and you aren't really missing anything by skipping it.