1. When you put a texture on a face, how do you know how big to make the image?
ANSWER:Texture resolution is irrelevant. The aspect ratio on the other hand matters but it is almost always 1:1 ie. a square.
2. What is the size of a 2x2x1 brick in Blender? (not for obj2blb)
ANSWER: 0.5 0.5 0.3.
3. How do I properly add a texture? (not a color) Whenever I try to do it, it doesn't seem to "accept" the face as it's "parent".
ANSWER:The easiest way is to separate the textured face into it's own object and apply the texture to that.
4. How do I split an object off?
ANSWER:Select the face and press P.