Shopping Cart details

Hi I am a new user to the shopping theme. So far so good.

I just have a couple of questions.

If my inventory is one off pieces. When the item is sold will it automatically be removed from the product showing on my shopping page? If no, how can i make this happen.

Also, If I want to show more than three items across on my products how do I get the theme to show more items per page?

thank you any info is great