1. The difference between 99$ package and the 159$ is just the PSD files. The PSD files are just templates that can be used by web designers to redesign the theme. Theme redesign can also be done without the PSD files.
2. If your language is listed here
http://www.appthemes.com/support/languages/classipress/ then it is just a matter of uploading the language pack files to localize the theme to your language.
3. You can remove the Appthemes credit link. Likewise, you can customize the Facebook widget to your facebook page account.
4. If you are just starting out and with minimal traffic, Godaddy will work just fine.
5. The theme will work just fine without plugins.
6. The default settings can be changed through the admin such as adding categories, making a custom form and etc. However, making changes on how the theme looks will may require some form of code customization.