[What are the things you should know when creating a complete avatar or a cloth?]

Hi. I am new in SL and been doing some practice in 3d using Blender 2.63, I would like to ask if you could help me answer the following:

 

1. What are the basic things you should know when you want to know how to create a complete avatar or a clothing?

2. Does "retopology" is a critical thing to be learned and what does it do? (I have gone over different tutorials/articles about this topic, claiming it is for beginners but never told why they should be learned and how do they work :-( ).

3.  Does learning Scripting is required in creating a complete avatar?

4. Does animation is essential in creating an avatar?

Thanks fellas.