Welcome to the challenge @chrihoonart! The more, the merrier.
Jellyfish would be super cute! I like your sketch at the top right corner. As for shading, you can go anywhere from light translucency (only edges shine some light through) to almost complete transparency. Up to you.
Shading will be tough for all of us, I don't think anyone here tried translucent characters before, that's why we came up with the challenge.
Here are the few things that could be used as helpers:
1. Art School class on Physics of Materials (Term 7, class 1)
2. References of the creatures to be mimicked. I will be using this step-by-step for crystals by @art_side_of_life (taken from Instagram):
Here's a good example of a jellyfish character from Art Station: https://www.artstation.com/artwork/ybL00K
I also like the simplicity, and high quality of this one: https://www.artstation.com/artwork/3LEzJ
3. If I can get my willpower together and dive into Zbrush more, I'm thinking of using modelling there as a reference for the final painting. Here's a tutorial on how to make separate subtools transparent: https://www.youtube.com/watch?v=DF3MFblYETM
Good job and lets make this challenge awesome everyone!