I received a largish (about 150cm high Acer Palmatum 'Deshojo' for my birthday this June. It was very full and bushy (maybe a bit too much - I wondered if it should be trimmed in the centre). It was also in an extremely small pot for a tree its size. So I re-potted it into a larger (and heavier, as it can get windy and the tree was blown over several times) pot. This was perhaps a bad thing to do at this time of year? We went away on holidays for the month of August. The person that stayed in our apartment watered the plants regularly. However, the tree is showing three signs of distress:
1. The outer leaves are turning brown, curling up and dying. I have since read that this is most likely due to the fact that it has too much sun exposure and not enough watering at the top of the plant.
2. MANY of the leaves are dropping off, even if they have not browned.
3, and worst. Almost all of the leaves are covered in a white powdery substance that was not there at the end of July. While spraying the leaves this morning with milky water, I noticed a kind of insect nest in two places (see bottom two photos).

How can I treat these problems? Please assure me that my tree is not dying (and that I did not kill it by re-potting mid-summer) ?

Thanks for any advice!!

Its healthy leaves look awesome!