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This article will help with common reasons for trees not leafing out: https://www.gardeningknowhow.com/ornamental/trees/tgen/tree-leafing-problems.htm

I don't think squirrels eat bark, but they might peel some off the tree if there were something tasty t eat underneath. This article has some insights into peeling bark: https://www.gardeningknowhow.com/ornamental/trees/tgen/peeling-bark-on-trees.htm
Since this could be potentially a serious problem, you could take some bark samples to the Extension Service for analysis and recommendation. This link will help you locate one: https://www.gardeningknowhow.com/extension-search/

The most important thing is to learn what is causing the yellow spots, whether a disease, insect, or mineral imbalance. The simplest thing is to take leaf and soil samples to the nearest Extension Service office for analysis and recommendation. This link will help you locate one: https://www.gardeningknowhow.com/extension-search/

Maple leaves should be wonderful for your garden. As the leaves are a little larger, you may want to pile them up and run them over with a lawn mower to help cut them up a little. It is not necessary but will help them break down faster once they are placed in the garden.

From this angle, it looks like some kind of scale. If it is scale, you will be able to scrape the little yellow things off with your fingernail. There are several types that can attack Japanese maple. These articles have a lot of information on the pest: https://www.gardeningknowhow.com/plant-problems/pests/insects/control-plant-scale.htm http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7408.html.
Of course, the best thing to do is to get an identification from an expert, who will also be able to advise you on the best treatment available to you where you live. You can call up a certified arborist.
If you're in the US, you can access the Extension Service in your area https://www.gardeningknowhow.com/garden-how-to/info/what-is-extension-service.htm
In the UK you have the Master Gardeners: http://mastergardeners.org.uk/get-involved/find-your-nearest-master-gardener/
Elsewhere, you can find the Master Gardeners, or a similar organization, through any botanical garden.

Did you have a dip in temperatures after the tree had began leafing out?
Since it was a newly planted tree were you maintaining a regular watering schedule to establish the root system?

If the branches or limbs are still pliable they are most likely still alive, if they dry and become brittle they have died off.
I would not give up yet, but continue to care for the tree with regular watering.
Best of luck.

Here is a link about Red Maple Trees

https://www.gardeningknowhow.com/ornamental/trees/maple/care-of-red-maple-trees.htm