To answer your questions backwards, there is a module out there that replaces the 404 page. I'll quote the author of the module:

"Instead of showing a standard "404 Page not found", this module performs a search on the keywords in the URL, e.g. if a user goes to http://example.com/does/not/exist, this module will do a search for 'does not exist'."

It's called Search 404. Here is the link: http://drupal.org/project/search404. I have used it on some of my sites and it works well... it's better than getting a 404 page.

Now you should have been able to rename the pages to what was on WordPress with no problem. I have done this as well. You do need clean URLs on the old site and on the new. Install the Search 404 and that should at least take care of people coming to a wrong or missing page.

I'll put a video together on this module for anyone who is curious about it. Look for that in the near future.