On MOO & Behavior Trees you'd still need the in-world MOO menu options for controlling creatures since the BT editor is more of an administrative/developer console. As a player you'd probably never interact with that editor directly, it is far more for experimenting with creating actual behaviors that could then be put to use in gameplay 
It may be worth checking out Dwarf Fortress (if you haven't already) to get the basic feel of how you control your dwarves there. I think the MOO UI was more or less a mockup of how you might build a controller UI, but it isn't the required way to do it. It may well be that a different approach is needed like @overdhose's old radial menu developed (but never merged, alas) for Miniions.
As for AI in general two things come to mind, although they both end up dealing with BTs
Edit: Oh, as for diagrams, mostly there are just videos showcasing some of these things. Not a lot of architecture diagrams anywhere I'm afraid, just some to show interactions with Gradle and GitHub. And maybe a rendering chart.
It may be worth checking out Dwarf Fortress (if you haven't already) to get the basic feel of how you control your dwarves there. I think the MOO UI was more or less a mockup of how you might build a controller UI, but it isn't the required way to do it. It may well be that a different approach is needed like @overdhose's old radial menu developed (but never merged, alas) for Miniions.
As for AI in general two things come to mind, although they both end up dealing with BTs
- https://github.com/MovingBlocks/Terasology/issues/2232 specifically the Light & Shadow creatures no longer reacting to their behavior tree config. I suspect this is a simple disconnection in config or code, as BTs definitely work and the deer are fine (if a little odd at moving) presently. Probably just need to figure out what's missing from the L&S creatures to follow their own commands.
- There is a new behavior available for Gooey in https://github.com/Terasology/GooeysQuests that lets Gooey follow you around. This would be something cool to examine further for later L&S usage, and probably useful for MOO as well. Gooey just follows the player at present if asked (via an `e` click dialog). Maybe something similar could be set up with the Dominog now available in LightAndShadowResources so it could be taught to follow the player on command (with the other L&S creatures having other commands to follow)
Edit: Oh, as for diagrams, mostly there are just videos showcasing some of these things. Not a lot of architecture diagrams anywhere I'm afraid, just some to show interactions with Gradle and GitHub. And maybe a rendering chart.
