Remove Tags Box and 1 Catergory Per Post

So when I user chooses to upload a classified I want

1) the "add tags box removed" how can I do this?

2) For them to only be able to use 1 Category and 1 sub category

And on the classified page I want on the sidebar (so a widget) let people click on the categories of post. Just like they can when a classified is posted and they can click the categories.