Better triac gate configuration
I've made a few triac-based incandescent lighting controllers and never used a resistor from gate to neutral.  Triacs are current-controlled devices, so they will stop being forced on as soon as you remove the drive current.

I'm sure you know that they latch on until the load current stops.

As for the size of the resistor, it will only see a short spike of current when the triac turns on.  After that, the entire triac is a short-circuit except for a couple of diode drops.  So R1 should be sized primarily to handle the voltage because the average power is still quite low.