As far as clipping first shoots,
I have let my first shoots go and never clipped. Last year a few plants got frost pruned and died back, but the plant threw new and the harvest compared to other years was the same.
A far as trimming to only two bines per plant,
I think it depends on what you are growing them on.
If on a line, it makes sense to limit to two bines.
If you grow on a fence with lots of surface area, I think it makes better sense to let a bunch of bines go. I agree with Denny, letting all the bines go does not affect production negatively.