1. Short answer is yes. The theme is not encrypted, so if you have the coding knowledge to make these kinds of changes, then it can be done. In terms of creating category icons, you can find a tutorial for this on the
AppThemes blog.
2. Sorry if I misunderstand your question here, but are you referring to creating ads in subcategories, and charging per category? Because yes, there is a "Price Per Category" pricing option.