Jeff, if it was my tree, I'd take the snippers and prune off all that twiggy stuff from dead dry leader and remove all but that one healthy strong right branch. Leave the stripped bare dead leader to be used as a stake and tie some soft rope around the remaining live branch and gently pull it upright towards the dead leader, do so in increments over a matter of months so that you don't exert too much pressure and break the healthy branch. By next summer that branch should be established in a near vertical positiion and you can then carefully cut and remove the dead leader.

I have 5 of the same type of trees and I too bought them on sale last year. They all seem to be doing great but have large low branches that are going to be a problem in a few years. Should I trim them next spring or try to train them up and out of the way?

It depends on how big the trees are now. It is actually of benefit to the trees in terms of helping establishment and developing trunk girth to leave lower branches in place for the fist few years on smallish trees. But you do not want to wait until the trees get too large or the branches that you will be removing get larger than about 2" in diameter.

And this link on the structural training of shade trees may be of help to you going forward.

ps. Don't even attempt to try and train the branches upwards and out of the way. It won't work and it won't be good for the tree

Trees are only abut 9'-10' feet tall and trunk is 1.5"-2.5" in diameter at base. Branches to be trimmed are 1" or less. Early spring before the buds form is the best time to prune, correct?

Jeff, about eight years ago, this 'Prairie Splendor' Norway maple had very closely resembled your tree with having lost its leader and looking downright sad, thus I considered removing the thing altogether. I did my above mentioned procedure and this how it has recovered ... well, photo was taken last spring and it has grown all that much larger. There only remains a small well healed over scar where the original leader had been.