Triac-Diac Dimmer build
These are nominal values for power, if you need less then there will be no major issues. But...the triac has a holding current, more powerful means greater holding current, meaning: when the current will fall below the holding current the triac will turn into non conductive mode, this is at th end of each cycle, while it starts conducting with a single pulse trigger. Therefore a larger triac will cut-off the power a little bit sooner than smaller one (but I wouldn't bother in your case).
If the load is inductive (your case) then the triac might re-trigger on accidentaly and to suppress this phenomena a snubber circuit is used.
In your schematics something is weird: C2,R1 is a snubber which should be placed parallel to the triac, not in that position where it is now (this is only my opinion). Look this similar schematics and see the arangement:
http://www.electronicecircuits.com/electronic-circuits/filament-light-dimmer-circuit