I would leave it till late winter/early spring. Just as the very first leaves breaks through the bud. That is the time at which you may work on the roots of the plant too. Make sure you spread the roots out nice and evenly, perhaps place a tile under them so they grow strong lateral roots, which will become your nebari for the bonsai.

Leave the reast of the plant as is, and let it grow strong first. Please have a look at how to grow trunks

Here is a link that might be useful: how to grow trunks for bonsai

Maple update.

I planted this maple in the ground last fall 2013.
Here we are, 14 months later.

In the last few weeks I have been getting new growth.
Meanwhile the foliage never came back on the upper tree.

I also noticed new growth on another Maple of mine late july/ august. But saw little to no action 6 weeks prior.

Do I cut off area with no leaves in the fall?
Thanks.

You can always cut off dead branches.

Winterfell - Thanks.
I may just do that this fall.

The lower portion of the nonleaf section is very much alive which is why I am hesitant to cut at this time.

I will however say I do like the new leader developing.
Perhaps by cutting the bare leader I can direct more energy to beefing up the truck and new growth.

I'd cut the dead branch ASAP. It's just a pathway for insects and disease.

I would consider letting it grow for at least a year, probably two, without any further action.

It is very small and experienced a great deal of die-back. Cutting any living branches until it is growing VIGOROUSLY would stress the tree and could easily kill it.

Spring is the time to cut deciduous trees for new growth, not now.