I had a pear tree (2nd year in the ground from bare root) that got broken by its deer cage which got knocked over in a heavy wind last summer. We just left it there, being busy with other things. It started growing back again, almost like a bush with lots of stems and leaves all the way up its remaining 18" or so of trunk. Before it got broken, there were only leaves at the top. Am I supposed to clip off all those wee branches? If so, should I do it now?
Not all of them. You need to leave two at the top they will turn up and form a new leader. Once they both turn up and you can trim the weaker one off. Others may disagree with me but I'd leave some of the lower ones until the leader grew up a ways. A plant gets its energy through it's leaves. As long as the leaves aren't shaded by other leaves and they aren't so dense that airflow is restricted they should help the plant grow bigger quicker. When the tree gets to the height that you'll want some branches and they develop you can cut the lower branches off.
Most fruit trees are grafted. A strong, disease resistant root and a nice fruit producing top. If the growth is from really low on the plant it may be from the rootstock, and you do want to remove that. You can probably find the graft, it may look like a sort of bent place in the trunk, usually just a few inches above the soil. Rarely more than a foot above the soil.