External Search module and results costumization

Hello,

I've not worked a lot with search modules, so I'd like to have experts' opinions and suggestions for a project coming up.

I most probably need to integrate the "external search" module into a client site.

The idea is to add extra search fields making it more of an 'advanced' search form (how can this be done? )

The functionality should be as follows:
- search query for third party site search request is constructed (whichever the third party site may be... it will not be google, nor any famous search engine or web directory)
- the request is sent
- The results needs to be obtained in drupal and a costumized search results page needs to be rendered

Any suggestions?