Well, I have two things to say:

1. Join game jam yourself and you can learn how it works. 

2. Having so many devs designing a game sounds like disaster. Different devs have different point of view, sense of design etc, it's not easy to moderate their ideas and designs.

I haven't started on graphical design yet.

TLDR, you should have this discussion with fans of the genre you're working on.

Make that jam now and let it min 1 month and lets see how it goes, we like the ideas.

just write the goals to manage game and let everyone who like to join making that rpg game.

blender 3d for models or reuse if already existing, assets even free and can bring in game.

avoid retargeting because lags, 1 avatar than add skins, edit motions  https://characters3d.com/search/animations

mods: no need of discord, we can publish assets in itch.io and strategic double programming ways are ok. 

3d engine, i use godot 4.5 is that a problem, there is a c# but webgl build  in unity we can understand.

gltf/glb/bin a character with height 2m and width 0.5m and grounded, and save import settings.

make the game and content to show the skills, not for resale but only free for non commerical, later episode 2 change. 

if progess in game dev wakes interess, there will be a lot joins, to the jams like:  https://itch.io/jam/brackeys-14/topic/5251825/steal-cookies-in-godot4-webglteam-level-up-play-great-puzzle-game-in-browser#post-13921920 just try out the pages see others how they add and jams like this.