I agree, 3 or 4 at a time is probably too much, I may have misremembered (I can't find the recommendation in any Weinberg book at my fingertips). But six month

I agree, 3 or 4 at a time is probably too much, I may have misremembered (I can't find the recommendation in any Weinberg book at my fingertips). But six months of solid work on 2, then six months of work on another two is an idea.