Each time I've been to Europe, it was easier in the long run (because I don't like carrying around large amounts of cash) to hit the cash machine like I'd do when I am home. Using your ATM at the cash machine will give you the bank's daily exchange rate and you don't have to really worry about it.
Otherwise, check your local bank. You can exchange cash at the airport, but it's not a great rate.... you pay for convenience, if you don't have the time.. it's worth it to se the airport. I'd probably get about 20 bucks worth, so you don't get off the plane wiht no cash, then hit up the cash machine at the airport.
Customs is really a no brainer, don't be a jerk, be polite and don't smuggle in any illegal drugs...
On your way out, declare what you've purchased... and you will be on your way.
Make two copies of the front page of your passport, and keep the copies in two different locations... just in case...