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A standard dimmer switch will easily control a traditional incandescent bulb. If you choose to use a compact fluorescent or LED bulb, you will need to install a "C dot L" dimmer, which is designed to control these lower consumption types of bulbs. These dimmers are readily available at home depot and lowes.
I would suggest construction adhesive which will attach the trim boards while also providing a capillary break between the block and the trim board so that moisture does not wick into the trim boards. I would also suggest installing the trim boards at an angle to shed water away from the house.