What to do with the /RST pin?
Pulled down internally means there is a pull-down resistor inside the chip. If it was an internal pull-up then you don't technically need an external pull-up resistor but may want one anyways for noise immunity.
Since it is a pull-down internally, you most definitely need an external pull-up resistor. The internal pull-down is probably a very high resistance so if you pull-up with a lower resistance it form a voltage divider where the voltage is still high enough to keep it out of reset.