How to customise the entries

I have set-up some custom fields but I want to make so other customisation.

We have two different listings and I want to have slightly different options for each.

1) Section 1 Listing description – where do I go to edit this? I can’t see it in the Listings set-up.
2) Categories – the list of categories to choose from is too big for our needs for the second listing. We want to force people into some very specific categories – so how can I reduce the number for that second listing. I can see how to edit them in the main Categories section in the Dashboard but is it possible to have different sets of categories for different listings?
3) How can I delete Image Display Settings.