It's hard to say. I would see how your historical fiction works go. If your fans see you as a historical fiction writer, then I would go with that for a period of time until you are ready to break out of that mold. I don't think you need to limit yourself but if you do decide to go another route, you'll need to do some marketing to show your other areas.
As far as a series, books that relate to each other would be a part of a series. If they don't relate in some way, then they would be separate.