Height reduction in a Japanese Black Pine

Hi! I just purchased 2 large Japanese Black Pines in good health, and have some questions about reducing the height of these trees. They are both between 4 and 5 feet tall. I have not worked much with pines at all, but my understanding is that any pruning should be done very gradually. The trunks of these trees each have an area devoid of needles and I would like the trees to backbud in here. There is plenty of top growth as well as some low branches.

How much should I be pruning these trees back this year? Should I leave them for a year after pruning before doing anything else to them. They are currently in plastic nursery pots. Should I plant them in the ground or into grow boxes? Is it safe to transplant them at all if I prune them this year - i.e. should I leave them in their nursery pots and transplant next year?

Any help would be much appreciated...I don't want to stress these great trees!

Thanks!

Oh...I should mention I live in southern Ontario, Canada and spring is in full force here!