The Sailor Stars in the Sailor Moon manga are not transgender. The manga portrays their genders consistently without any indication of them being transgender.
Sure, the Sailor Moon manga is finished. It wrapped up nicely, giving closure to all the characters and their adventures. But you can still enjoy re-reading it or exploring related merchandise and media.
In general, Sailor Moon Crystal is a faithful adaptation. It keeps the key elements and storylines from the manga intact. However, there might be some minor tweaks for the sake of animation or to enhance the viewing experience.
The number of Sailor Moon manga varies. There are the main series, along with special editions and adaptations. But as of now, I'd say there are at least a dozen or so.