To start with, those main image and alternate images which is called "Switch", we need an admin to put MediaWiki:Common.js from here and then create 2 templates which is Toggle and Switch itself.
AAANNNNDDD, from what you've said: "as for the main image and alternate image, I'm guessing its for the character and their shoukanjuu form then?" it seems to be not a bad idea, so let's do it.
And and AND and, yes. For the image gallery, just create the character's image gallery without the tabber. Sorry :(.