美少女戦士セーラームーン 1

There's a few potential stumbling blocks with this series. The fantasy vocab will likely all be new to you, since it's stuff that certainly isn't taught in textbooks. The primary villains talk in Typical Anime Villain speech, which is archaic and, again, not taught in textbooks. But other than that, it's not all that difficult, and all kanji do have furigana.

To get the most benefit, I recommend watching the Sailor Moon Crystal anime alongside it. Because the new anime follows the manga so closely, if you read a manga chapter first and then watch the anime episode right after it'll be like you read the anime's script beforehand, so it makes understanding the episode that much easier and you get listening practice for the material you just read.

If you like Sailor Moon, reading the manga is a decent way to practice your Japanese. If you don't already love Sailor Moon, however, I doubt reading the manga will change your mind because the story is fairly predictable and shallow and the character development is pretty shallow (early on, anyway).