Customize Mosets Tree Search Module

I would like a small customisation to the Search Module in Mosets Tree. In the default Search Module, there is a Search Text box for the user to enter their own text, plus there is a Categories drop down box. What I need is: 1. Remove the Search text box 2. Add a second drop down box that will contain sub-categories of the category chosen in the previous Category drop down box. 3. I have added an additional drop down box that references a custom field (location). This is working nicely, but I would appreciate a review and possible clean up of my code. Or if it is easier, just re-write it your self. Please see attached image for how I have customized it so far. The first drop down is the categories, and the second is the custom field.