Yeah, there is a learning curve on pines (she said ruefully...)
They are tough, but have very specific needs, one of which is to not overwater them. They like drier feet, and if you keep them too wet, they will die. Where are you located? I don't know that black pine can survive in the ground in very cold zones...
But it does look like it would benefit from some accelerated growth. You could do a grow box, or large training pot. And I would wire some movement into it as soon as possible, before it gets too hard to do. Just make sure you keep an eye on the places you wire, so that when they grow, it doesn't dig in and scar the tree too much.
You should do a ton of reading about how to manage pines, but if you will develop this in the ground, keep in mind most of the techniques to make smaller needles will not apply to this tree until it's in the final stages of development. (in a pot)
Be aware that there is a lot of contradictory info on pine management, there are all kinds of different ways to do things. I think that pines techniques are very subject to climate of the area it's being grown in. So maybe you could find some information from someone who grows them near you. Things that can be done in California to pines wouldn't work as well in New England, and the timing is different too. Maybe a club near you?
