What are the rules for submitting custom items? Do they *have* to be equipable and useful (in a RPing sense, obviously)? Can I submit a custom image for an exotic orchid my character acquired or a rare painting? A forgotten statue perhaps? Or this is against the rules?
Yes, you can submit any of those things. The item doesn't need to have any particular use, and most don't. It doesn't need to be something you would normally equip, although I would recommend allowing for hand slots so that you can carry it..
As far as I know, there are no limitations to what you can create. You can't create a gun and then expect to be able to use it now or in the future, however. The feature was added specifically to allow people to create RP/flavor items.
I dare you to make less sense.
Are you a newbie, or do you have access to newbies?