Yes, in your configuration you will need all grounds connected together.
You're also going to apply a bit too much gate-to-source voltage when the P-channel MOSFET is turned on. A 24V difference may even damage it. I'd recommend adding another resistor in series with the BJT collector terminal to form a voltage divider with the 10k resistor and get the gate-to-source voltage to be about 12V (so another 10k resistor should do it).
Otherwise it's looking reasonable.
The MegaRAM shield
: add 128 kilobytes of external RAM to your Arduino Mega/Mega2560