Double check with time machine to make sure everything you want is backed up. Or, just back it up again to play it safe. Then do the clean install, then there should be an option that says you can restore from time machine backup, and then it'll transfer everything, which could take at least a couple of hours depending on how much stuff you have. After it finishes, everything should be exactly as it was before, same preferences, passwords, data, etc...Only thing is, there's a small chance you might run into a problem with a couple of manually installed applications (from cd or serial number applications).