The Meaning of Life, the Universe, and Everything.
If this is your first time creating a pack, then the best way to start is using the default Minecraft assets. Use this link to start, but go into .minecraft/versions/(version you're making a pack for/current version) and use 7-zip or WinRAR or something similar to convert the JAR file into a folder. In the folder that is created, there will be a ton of files. Find the assets folder, and copy that instead of creating an assets folder like in the tutorial.
For sounds, I'm not sure...I think it says on the tutorial
It covers 3D models on the tutorial. Just skip all of the extraction steps, you already have those files.