Some questions :

• how to have a global view of the id's and classes used on different pages ? go trough the pages and collect them, building the style of the site incrementally pages by pages ?

David: See the theme_howto

• Is there any free tool to edit css easily (i already know the webdeveloper toolbar in firefox) ?

David: I usually use my text editor, but you can have a look to Quanta or Nvu. I guess there exist others but I don't use them.

• Any advanced free tool to work with php ?

David: Have a look to Quanta perhaps.