All of the questions you have asked have been answered many times. Read up on the FAQ Emporium, it has alot of information there.
as for you questions, weather does affect you car pc very much. In the winter time some hard drives are not able to spin up to load up windows. Most people recommend using a laptop hard drive since they are better designed to take more abuse, but many people including me use a regular hard drive and haven't had any problems.
btw: you should really attend the meet you will get some great ideas and people will be able to help you better. Heres the link to the meet thread.
NY (area meet) July 10