The only suffix that you can definitely say is feminine is "-iel." "-eth"
can be feminine, but it isn't 100% feminine.
BW, I would really recommend this site:
Ardalambion
It has extremely detailed descriptions of just about all the languages that existed in Middle-earth, even the ones that he barely touched on. There is also a Quenya course that you can download, which greatly helps Middle-earth language students. It's the course that I used to learn Quenya.