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No, it is not normal. I would treat the tree with neem oil, which is very effective for most insect pests and should take care of any fungal issues that may arise as well. Here is more information: https://www.gardeningknowhow.com/plant-problems/pests/pesticides/neem-oil-uses.htm

It is really, really hard to overwater a newly planted tree. Unless it is sitting in standing water, it is not getting too much water.

It may have transplant shock. This article will help:
https://www.gardeningknowhow.com/plant-problems/environmental/learn-how-to-avoid-and-repair-transplant-shock-in-plants.htm

You can try spraying what you can reach with neem oil. It is an organic, people safe oil and the nice thing about it is that the tree will absorb it and carry it up to the parts of the tree you can't reach and kill the pests there.

For a truly non-chemical solution, you can try predators such as Aphidolytes or Aphidius. These are midges that prey on green fly and will kill them. They should be available from reputable plant nurseries.

Here is an article that you may find helpful: https://www.gardeningknowhow.com/ornamental/trees/tgen/what-is-tree-sap.htm

Yes, this sounds like powdery mildew. Neem oil is oftentimes effective. Here is more information: https://www.gardeningknowhow.com/plant-problems/disease/powdery-mildew-homemade-and-organic-remedies.htm
https://www.gardeningknowhow.com/plant-problems/pests/pesticides/neem-oil-uses.htm

You can do a process called topping, which will encourage a tree to grow out rather than up. It is not normally recommended because it shortens the life of the tree. This article has more information on the pros and cons: https://www.extension.iastate.edu/publications/sul7.pdf

Sugar maples want to grow rather large. You may not be able to contain its growth to under 10 feet, even if you top it. You may want to look for another variety of tree to go there, such as a small ornamental.