I think it depends a lot on variety and environment. If I were you I would let them go with whatever they produce, given they were properly spur or cane pruned prior to this years growing season. If you havent been pruning them while dormant, you WILL need to remove a lot of fruit if you want anything to develop at all. Adjust how you do it next year based upon what you get this fall. Might need to do a combination of cluster and berry thinning to get optimal results.

How do you plan to do berry thinning, gibberellic acid? I've tried that once or twice. Have also used it after thinning to size up the berries. But it's not something I want to bother with again.

I thin to one cluster per shoot. But as Derek states it depends on how many buds/shoots you left to fruit.

I've never felt I over cropped young vines but I'm pretty conservative on crop load. In a cold climate over cropping could come back to bit you in the form of winter injury or otherwise.