Adding a switch would not only be nice, it's practically necessary. Unless you want to be turning the breaker off whenever you want to work with the wiring in your ceiling box, put in a switch. Plan beforehand whether you want a single switch or you want the fan and light switched separately. 14-2 for single, 14-3 for separate switching. Generally, most electricians connect the red wire to the light (red to blue), and black for the fan.