The Si2356 is a good choice for a 3.3 volt gate control. It will have an on-resistance of about 0.05 ohms and that is negligible compared to the 499 ohm resistor (R3) so 20 mA will produce 9.98 volts across R3. The impact of 150 k in parallel with R3 is also quite negligible (it'll drop to 497.3 ohms) so the real voltage developed for 20 mA is 9.95 volts.
When using it as a voltage potential divider there will be anything from 1 uA to 10 uA leakage into the "off" MOSFET but, in comparison with the current though the series combo of R1 and R2 isn't a big deal.
R1 and R2 convert 10 volts to 3.329 volts but beware of resistor tolerances. For instance, if using 1% resistors for R1 and R2, 10 volts in could mean the 3.329 volts is a bit higher at nearly 3.4 volts. I don't think it'll cause a problem other than the uncertainty of value. I'd use 0.1% resistors if it is critical for performance.