As Jørgen implied, you could have pretty much anything other than snow and ice. It could be glorious with temperatures in the 70's or more with not a cloud in the sky or it could be grey, cloudy and wet with temperatures in the high 50's, low 60's. Most likely it'll be a mix of the two.

Money... Use credit cards or go to ATMs to get Euros. If you are more comfortable having cash in your pocket then buy the Euros before you come.

Any tips... Don't tip the usual American 20%. 10% is fine all over Europe.