Cathy I dont know what your experience is but have you read Dick Arentz book? I dont know that you really need a metrolux timer but if you wish to get one you dont need an UV filter. If you wish to use it in the sun you will need a ND filter to lower the sunlight intensity. You can use it on top of the metrolux cell and it will "integrate" the light intensity. For a mercury vapor light I would also recomend a ND filter to attenuate the light. Basically what the "meter" will do is measure the intensity of light, if it goes lower it will "increase" the time, etc etc...color of light has nothing to do with the process although it is related to the amount of UV light.
IOW you wont be measuring amount of UV light, you will be measuring the intensity.
I recommend you first do your standard printing time and distance according to Arentz book and then worry about the "timer". Or you can always do ziatypes...