Yes, of course you can use it, this is the whole point of OpenGameArt :) Check the license field next to this asset, it tells you how you can use it. This asset is released under CC-BY 3.0 http://creativecommons.org/licenses/by/3.0/

Hello, the credits should say the license and the author. "CC-BY 3.0 Blender Foundation".

It's nice to see people find the sound useful. I wish you good luck with your game.

This sounds like regular snapping and it's something you can already do in Blender. You need to make a set of pieces that fit together at their border. You decide on the dimension of the pieces, i.e. 2x2 Blender units and then you place them in a grid as if they were tiles. You can also snap one object to another object's vertices to get a perfect fit (presuming the pieces were made to fit)

Blender won't restrict you when rotating and placing objects unless you tell it to. While the constraints to have a perfect grid are always there, the grid also needs to be in the artist's head so he/she knows where stuff should be placed.

Ok, here's the longer reply I promised.

1. Utterly simple rigs. With rigs, you can use whatever gets the job done. Your current animations seem to be working well enough so there isn't any problem per se. However, these animations have keyframes at every frame and are also short. With longer animations, you set keyframes at specific key poses, then define transitions with additional keys and curve editing (in Blender's graph editor). For this, simple rigs can be a pain to use and even harder to get right. In the end, rigging is about making a tool for the animator to animate the model, the easiest and most efficient way possible. Personally I wouldn't go below the level of complexity seen in the tutorial, simply because it's so much easier to work with.

2. More explanation for the tutorial. I'm happy to hear your feedback here to know how to improve the tutorial. I'll go over the it in the near future and try to explain the whys.

3. Opinion as an animator. Rigging depends on the situation and limitations. Game engines have a certain limit of how many deforming bones can be in a rig, while movies throw limitations out the window. UDK has, I think, around 60 deformable bones per rig + helper bones. Quad-bot from Mango open movie has insane ~800 bones. http://mango.blender.org/rigging/rig-detail/ The rig is made with a combination of bones, bone constraints, drivers, python and bone shapes.

• Bones are bones.
• Constraints define how bones or objects affect one another. Everything in Blender is animateable and so are constraints. This allows to animate their values and influence and e.g. swith between IK and FK rigs.
• Drivers take one object's property - (whichever, position, scale, rotation, slider, etc.) and have them affect another property of some other object or bone.
• Python is used for custom UI, buttons to toggle bone layer visibility and other.
• Bone shapes are when you use a mesh to substitute how a bone is drawn. Instead of octahedron, stick etc. you can have any shape you want

4. New base human. I've been working on such a thing myself, to learn and to eventually use it for something. If you need it I can release is as free art.

 If you have any more questions or suggestions, don't hesitate to ask.

Lamoot