Here's the work I did on a Schefflera this year:
http://bonsainut.com/index.php?threads/hawaiian-umbrella-restyle.19389/#post-279354 I left some leaves at the apex because I wanted to give specific buds a head start before removing all the old foliage. I have cut other trees back very low, in the spring and summer, all have pushed new growth. I'm going to cut another one back this week, because there's a lot of sun and heat left this growing season in my area.
I've noticed that new leaves are easily scorched when positioned in direct sun during summer. As others have said: filtered light. I was probably over cautious by setting this tree in the shade for 2 weeks after cutting back, only allowing it soft early morning sun. I misted it in the mornings and evenings on top of watering regularly, some times twice a day when hot. After the new growth hardened off, I gradually increased the duration and intensity of light choosing positions where it received direct light early and filtered/dappled light as the sun moved overhead, shade in the late afternoon. Too much shade and the leaves will grow to big and the petioles will elongate too much. I suspect 50% shade cloth during summer would produce the desired results; I use 50% shade cloth over my stock in development.
Aerial roots can be 'encouraged' by very high humidity and/or wounding the branch. I have seen roots grow at wound sites without applying rooting hormone, I just don't know if applying the hormone actually increases the probability of root production. I've read somewhere that aerial roots tend to form when the plant is pot bound or the roots are stressed due to lack of moisture or pruning or both. Sorry, I don't recall where I got that info.
I brought this tree inside and kept it in the guest shower on a bench during the winter. I used this shower, and the tree responded well to the higher temp and humidity. Once the night temps were consistently around 50, back out side it went.
I would leave it outside after cutting back, as the tree will benefit from the higher humidity. I have 8 other Scheffleras ranging 1 gallon and 15 gallon that stay outside in my area year round. I had 4 nights at 28 degrees last winter, many other nights below freezing. They seem to be tolerant trees given a healthy root ball. However, I would not leave any tropical in a
bonsai pot unprotected and where temps dip below 40ish.
hope that helps