Watering a Japanese maple is not rocket science, but keeping adequate moisture is crucial. In the tree world Japanese maples are considered shallow rooters. Most feeder roots are within twelve to eighteen inches of the surface for well established older trees. Newly planted trees can have all their roots much shallower than that.
Japanese maples like even soil moisture. On most varieties their leaves are very thin and will dry out and burn quickly when soil moisture is not adequate.
Tip 1 If the tree is planted in the spring, newly planted trees should be monitored daily. Check soil moisture a few inches below the surface. (How?) Water every 2-3 days for the first month. After that, a good watering once a week should be sufficient, but monitor it often as windy days can dry out soil quickly. If the tree is fall planted, water once a week when no rain or snow cover is provided.
Tip 2 Always provide a layer of mulch around Japanese maple trees. This will aid in reducing soil moisture loss due to evaporation. Since the roots are so shallow, the sun and wind can damage the shallow roots if not protected.

I missed judged your question. 
Wetting the leaves can encourage disease and insects. Instead, you should water the soil directly below the foliage, but not past the drip line, unless the tree is newly planted. You should also avoid wetting the trunk or the base of the tree within two feet.

See the answer above.
You can relieve drought stress by watering your tree from below without watering the leaves or trunk.
Mulch will also help to retain moisture.

Yes.