As far as tracking them (disclaimer I've never actually used this before) I don't think you would need to compare people's individual cookies to any sort of data (logs, dbs etc) but as you stated you would probably want to use a DB for keep a log of people

Just for tracking you could set a date in the cookie to see when they last visited. You can use $ENV variables to get the page their on, their IP address and tons of other information.