Simple fixes:
1. 10mA minimum is a good point to start reasoning from. 20 or 40mA typical would also be fine. It's not like it's critical. Certainly nothing to get pedantic about. (I say this, and I'm one of the biggest pedants here!)
Current is also limited by dV/dt, since I = C * dV/dt. 10mA into 10nF is 1V/us, a bit slower than the LM324 is, so the resistor will be useful (i.e., it will have a worst-case voltage drop near half the supply voltage, so it's doing something, and it's not too big, not too small).
If the gate were, say, 1nF or less, it wouldn't be a big deal, because the LM324 can't move that fast in the first place. A 100 ohm resistor would be fine: mainly to avoid possible oscillation. (External compensation would still be recommended.)
2. The LM324 will not blow up. It might get warm if it breaks into full oscillation. Even in a short, it's rated for "continuous" duty. You have to work to destroy one of these (or, as the phrase goes, "it takes a special kind of stupid"...
).
3. The transistor won't blow up. 15V is well within its rating.
That said, a G-S zener diode (preferably a large one, like P6KE15.0A or SMAJ15A) will help keep G-S voltage within limits, even under surge conditions.
That is, consider what happens when you connect a large 50 or 100V capacitor to the load terminals: the voltage rises within nanoseconds, limited only by series inductance and circuit damping. The peak current, during that transient, may be many amperes, and a fraction of it will be seen by the LM324 because the transistor has so much capacitance.
Designing the circuit around transistor failure is also handy; in that case, you might make the series gate resistor, and source/shunt resistor(s) fusible types, and add a protection diode to the LM324 output pin, so it doesn't get damaged by transistor failure (i.e., suppose it fails D-G shorted, S open).
4. If low supply current consumption is not necessary, then a pull-down resistor will stabilize the LM324's crossover distortion under quiescent conditions. Step changes in one direction will still be messy, but it will eventually settle out of it.
This, by the way, is another handy feature of "single supply" amps: they are well behaved on VEE-referenced resistive loads. In this case, it keeps the high-side output transistor active, so it behaves like a simple emitter follower. Only when the output needs to change rapidly, will the low-side transistor be turned
Tim