FOSS gamedev and creative worlds

I'm trying to make a new mesh model for a new mob I'm making.
The tutorial at the wiki says I should join all the objects together to make the texture. I did that and the object now has a texture png.

Here comes the animating part, the skeleton was detached because of the join operation, and I can't move parts of the model (arms, legs) because they are joined into one. How do I move them separately? Do I unjoin them? The animation part of the tutorial did not help in this case.

Second, how do I trigger animations in Lua? I see a set_animation function, but that seems to be for spritesheet (2D) animation.

Also, how do models scale in the game? How large in-game is a 1x1x1 cube in Blender, and what does the visual_size property do?

Thanks!

Ok, I managed to solve part of the problem by using the Armature modifier instead of using bone parents for objects (which was my initial attempt). The objects are really supposed to be joined into one. Then vertex groups + bones are used for animation. The Animation part of the Using Blender tutorial was not specific enough/vague/incomplete (for noobs like me!). Can someone please edit that page to be more noob-friendly?

Edit:
The visual_size property sets the size of the object in-game. It does not matter if the Blender object is 100x100x100 or 1x1x1, the game rescales it to fit visual_size. But I wonder why visual_size only has x and y, and not z; and I can't fully figure out how it works.

The last problem I have now is animation. I set the all animations in one continuous timeline (as said by someone in the forum). I still don't know how to trigger animations.

I'd check out the simplemobs mod, as I know that has animation for the animals. I don't know how to trigger them myself, but I did create a goat and animated it, and everything worked with that.