Usually, a cocktail reception is somewhere between 4:00 and 7:00 p.m. and includes hors d'ouevres. Although, any event that is going to start at 7:00 p.m. should include full meals. The open bar is your choice. Just make sure you understand your options.
The charge for open bar is either by consumption, hour or package. Remember to factor in that people who do drink will make up the difference for the people who don't. I've had many couples unpleasantly surprised by the bar tab of an 'open bar'.
As for the musical entertainment, you can use a D.J. or band. Rhonda Allen, Bridal Consultant New Beginnings Weddings