I will try to answer these in the order you posted them.
In order to create the pages with DataAssist you will need to have a connection to your db. Once the pages are created you will only see information that comes from your db. If you are connected locally then you can test the pages locally.
You can put the search form onto any page, it should always post to the results page.
If you would like to make a text input into a select list you can just update it to be a select list. So long as it contains valid values and the form element is named the same it will work the same.
I'm not sure about the question being asked in #4, please explain a little on this.
If you have a footer div in your template this should be in the same relative place all the time. If you want to make the content area a fixed height you should specify this with css.
To add the other search you should first create the search and results page with DataAssist, then you can add the new search form to your existing search page.