I have just bought the Super Pack to design a website and webstore for our small business, and it's great, it's got everything I need

First question: To ensure this continuity, I am presuming I should be using themes. A) If I purchase a theme or use one that came with VSD, can I edit it (colours graphics etc)? I am under the impression I can do this, using WIS but B) how do I edit themes in WIS?
Second Question: If I don't purchase/use a pre-existing theme, if I create my own page from scratch, how do I ensure that the basics on each subsequent page are the same (layout, colours etc)?
Third Question: How do I ensure that my theme can be used in the Shopping Cart Designer? If I purchase a theme from Coffee Cup to use in VSD, how can I know if I can get the same theme in Shopping Car Designer?
Thank you for any help offered towards my understanding
Rachel