yep James is right, it's a good idea to go to a few gigs and see how it all works.
a lot of it also depends on how you like to work the crowd. some bands go right into the music and don't talk too much in between songs. some bands like to work the crowd between songs, and if they're good at it and have a responsive crowd, it can work really well. if they're bad at it, it can backfire pretty badly on them. if you talk less you can play more.
it also depends on how long you take to set up. slow setup means impatient crowd and less songs to play.