if airfield is Cat2/3 then we require a Cat1 alternate within 1hr single engine flying time (around 400nm for our fleet).
As long as the airfield minima state that we can, then with the required training, lighting etc, we are allowed to depart with 125m otherwise most airfields we operate into the min RVR required for T/O is 150m.
At the end of the day the TAF means nothing to me,bar a heads up of what the weather might be like (when thinking about departing). Actuals are king!