Making new tileset

I’m currently working on a new tileset based on Chibi_Ultica.
The main difference from existing tilesets is the display of character sprites. I love old RPGs, so I’d like to make one featuring them.

Below is a demo version created as an add-on MOD for Chibi_Ultica. (I am a native Japanese speaker, so there is no English document yet. sorry)

This is my first time making a tileset, and I’m not sure how to do it efficiently. If you know a good tool or management method, please let me know.