Wordpress: Customisation of a theme

I need a theme designed for a real estate agency modified into a general directory. The meaty bits:

a) At the moment, one can filter by properties to RENT or BUY; I need these categories to be changed, with a few additions.

b) These categories have sub-categories that also need to be modified.

c) I need to be able to add new sub-categories from the back end

PHP intensive.

Start Date: two weeks from now.