As far as mods and map files go...
Only the creater of the game actually needs to have them when he starts the game, though everyone would need the .tga obviously (or not...).
Though it is likely in everyone's best interest to have the mods/.map file to run any testbeds that they want to.
As far as me being aquatic goes... since we have someone interested in Ryleth I suppose that would default me to Atlantis, which is fine, just so long as the map has enough water for the both of us
I'm still happy to take Jotun though if there is anyone who really doesn't want any aquatics in the game.