If you followed my instruction about permalinks you need 2 more plugins to finish the job.
.HTML on Pages
The .HTML on pages plugin automatically append .html to the wordpress “page”(s).
Traling slashes
The permalink trailing slashes fixer completes the job adding a trailing slash to category URLs and other links that does not ends with .html.
NOTE: this plugin require a little patch, see here
Top level categories
The top level categories plugin allow you to avoid them to appear under the root of your URL instead of under the “/category” path.