The P-Channel Mosfet symbol arrow uses conventional current flow (+ to -).
The reason for the pull-up resistor on the P-Channel Mosfet gate is because without the switch closed the gate voltage will be 0V causing the P-Channel Mosfet to always be passing current.
The P-Channel Mosfet needs the Gate voltage to be lower than the source voltage by at least -0.43 (VTO) to turn on.
P-Channel Mosfets are easier to use on the high side before the load.
