You can program the Raspberry Pi with BrickPi+ using just a 5v power supply (as long as it provides enough current that the Raspberry Pi is stable).
However, if only running on 5v, it is best to not run motors, and a couple sensors might not perform as expected. For running or testing a robot after you have programmed it, it is recommended that you use either a battery pack or a regulated wall adapter that can source enough current for the Raspberry Pi, BrickPi+, and any sensors and motors you are using (note that each Lego NXT and EV3 motor can draw up to about 1A under heavy load). The power supply should be about 9v (7.2v-12v should work, but the motors are designed for 9v).
It should be fine to have the Raspberry Pi connected to a 5v power supply at the same time as the BrickPi+ is connected to a 9v power source. Running like this has the advantage of the BrickPi+ being able to keep the Raspberry Pi running stable even if the 5v USB power is inadequate.