Whilst learning programming, I wanna talk and ask about something

I wanna learn the mechanics and codings of Ragnarok Online
NOT because I wanna make my own private server,
BUT because I wanna design a JRPG which has unique colour palette, visual equips of 2D sprites, four battle system(duel, brawl, skirmish and strategy) and rotatable 3D over 2D sprite camera.

How best do I do this, besides directly modifying and overhauling the RO client?

join here

https://herc.ws/board/forum/118-development-discussion/

for hercules packages

or

rathena source and package :

https://github.com/rathena/rathena

get

Thank you. I suppose starting there is pretty much the best option for learning the coding side of RO