In addition to that payload sticker, you'll need the info in the manual to get accurate information about hitch weight limit and actual towing capacity. Things like cab configuration, gearing, 4wd vs 2wd, engine size, and option packages change the towing capacity from a stripped down model. The manual will have a chart that shows you what your configuration is rated for.
Fortunately the Internet is a wonderful thing and most manuals are free downloads: 2006 Ford F-150 Owner's Manual - JustGiveMeTheDamnManual.com
. This link is pretty safe, I have downloaded manuals from there before.
And don't be paranoid. Just have fun!