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Peach tree borers can sometimes cause this problem. Here is an article that you may find helpful: https://www.gardeningknowhow.com/edible/fruits/peach/peach-tree-borer.htm

No you do not need two peach trees for pollination to occur. The blossoms will pollinate each other on one tree. A peach will not cross with an apple either.

Some trees, like peaches, may be slow to start if they do not receive an adequate chilling period in winter. Here is more information: https://www.gardeningknowhow.com/edible/fruits/peach/peach-chill-hours.htm

How often are you watering? Trees need significant amounts of water their first year. I would recommend increasing watering, as it is either a watering issue or a nutrient issue. Make sure the tree is getting water daily, twice a day in temps over 85 F. And give it slow release (balanced) fertilizer that will continually feed it. This article should also help: https://www.gardeningknowhow.com/edible/fruits/peach/fertilizing-peach-trees.htm

Some trees, like peaches, may be slow to start if they do not receive an adequate chilling period in winter. As much of the country experienced a fairly mild winter, this could likely be the reason behind your tree's leafing out issue. Here is more information: https://www.gardeningknowhow.com/edible/fruits/peach/peach-chill-hours.htm

The tree should be fine. Don't put anything on it though, as this can cause more harm than good. Tree wounds will generally heal themselves. The following article should be of some help to you: https://www.gardeningknowhow.com/ornamental/trees/tgen/repairing-tree-bark-damage.htm Just as a precaution, keep an eye on the tree for any signs of pests or disease around the damaged area. If you spot anything, treat the wound with a fungicide like neem oil.