MOSFET Circuit Design and Thermal Considerations
You have mostly thought this out correctly.

One problem I see in your figures is the power dissipation of the FET.  You say the gate will be driven by a 3.3 V digital output.  The only guaranteed on Rdson is 135 m&Omega; at 2.5 V gate drive.  You can't use the 105 m&Omega; figure since that's for 4.5 V gate drive.

The power dissipation will be (500 mA)2(135 m&Omega;) = 34 mW.  You will have difficulty noticing that get warm.  It's not anywhere near any limits.

Inrush current will be much larger than the steady 500 mA operating current. However, it won't last long, so it looks like you'll be OK.  Note that the maximum pulsed current this FET can handle is 6 A.  That sounds sufficient at 12x the operating current.  Of course the dissipation will be quite large then, but again, short lived.  Without details on the motor, we can's say for sure, but I think you'll probably be OK.

It's good that you put R9 there, but I'd make is smaller.  100 k&Omega; will do a better job against noise that might be picked up, and is still of no consequence to your digital output.

If you plan to switch the pump on and off rapidly, I'd use a Schottky diode to get around reverse recovery time issues.  If you always leave the pump off for more than a millisecond or so, then this doesn't matter.

I would also put a small cap across the pump, especially if you aren't going to switch it rapidly.  That will help with RF emissions.