You may also consider a 325W ceramic metal halide (cmh). They have a very good spectrum +uv etc etc and it seems the perfect size for what you are doing. If you start running over night that will offer better control over heat in the summer while in the winter the heat would cut down a lot on having to use a heater 24/7.
Install a fire alarm as close as possible and have two thermal cut out leads to spread load. Wound up extension lead in a hot environment is bad even if under loaded. I would take this part serious because in a small room like that if something goes wrong, like a timer fk up, it will get very hot very fast. If it's an open cupboard type of deal then I guess you can regulate the heat from the big room/s and little of the above is a problem, but 100% use thermal cut outs if not already.
Look in the vert forum if you think that style may serve you better with the vertical vs horizontal space you have to play with. Just make sure to check bulbs and fittings can handle being hung that way should you miss that disclaimer there and decide to try it. The box fan under light would also be a necessary addition in that style should you also miss that.