AppZapper works great for deleting all the prefs and things. It is very simple to use and has a window that pops up showing what files it thinks should be deleted so you can verify it before it proceeds. Check out their site; it will show you a screen shot of what it looks like in action. I think AppDelete works similarly and there are other products out there as well.
Not sure about your second question, sorry. I have always kept an eye on my uninstalls so I haven't had a need for it. Aside from some clutter I don't think orphaned files can cause any problems because OS-X does not have a Windows like registry that it has to parse through during startups, installs, and God knows how often in between. If you can't find anything that can scan your system for old, unused app files, you can take a peak in your Library-Application Support and PreferencePanes folders for related junk files if it makes you sleep better. Unlike Windows, OS-X does not suffer the my-system-is-slowing-as-the-months-pass syndrome. Although, to be fair about it, my Win7 box at work has shown no signs of slowing so perhaps Microsoft has worked out those bugs.