I don't really know if you will be able to take expert down without dying if your power is below 15k. Probably not. So my suggestion would be to get stronger by leveling up weapons and eidolons that you are using to at least level 10. If possible replace that normal and rare weapons with SR or higher. (You have chance to get SR weapons from raids if you are the one who discovered it, was mvp or vice mvp. Also if golden chest drops.)