chasing lights type pattern, where one turns on, then the following one turns on as the previous shuts off
Eyes are tricked very easily. With 3 groups of LED's you see the movement, and you can even play with different duty ratios:
Having either lights or "black holes" moving around
(For symmetry you'd need 12 or 15 leds, though)
more to power Arduino as well, and, if so, how much more
Arduino itself takes about 40 mA, I read. If it's regulator gets 9V, about 4V40mA are producing heat in the 5V regulator, 5V40mA are producing heat in the controllers (and the 3.3V regulator, and the power indicator, etc).
If you run 2*7 LED pairs in series, they have to share the 5V and probably won't take the full 20mA, you might even get along without switching transistors. Just tie the series pairs to pins 2..8 and see if the brightness is sufficient.
(To be on the safe side, test a single LED in series with a 120 Ohms resistor and verify the voltage drop is about 2.5 / 2.5 and the current is ok)