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Simply cut the trunk with a sharp pruner, or saw if too large for pruners. That stem will send out shoots near the cut area. When they start filling out, cut another, and continue until the plant is much shorter. I recommend making the cut way below the height you desire, as much as 2 feet. If your plant has a lot of stems, this may take a while, but when finished, you will have a shorter, thicker plant!

It is possible that the leaves were old and going to drop anyway? Sometimes, there is a huge shock in some way or another, and there will be a leaf drop. It's possible that it was delayed. I wouldn't imagine that a foliar application of fertilizer would cause leaf drop unless it was very heavily concentrated, in the sun, and applied several times. You state that the new leaves did not shed. That's good. Continue watching for new growth. personally, I wouldn't worry too much unless more leaf drop occurs. I also wouldn't foliar feed when the plant is dry or temps over 85*. A drench or light foliar misting would be my choice. I prefer a well balanced fertilizer, 14-14-14 instead of vast differences of NPK%.

The following link will take you to several articles on houseplant propagation: http://www.google.com/cse?cx=012078378210706707791%3Af1h5n_k1r5e&ie=UTF-8&q=blackberry+problems&oq=blackberry+problems&gs_l=partner.3..0i8.134411.138674.0.139862.19.14.0.5.5.0.187.1725.2j12.14.0.gsnos%2Cn%3D13..0.0.4333j1257669j19..1ac.1.kQAzbvAmZA8#gsc.tab=0&gsc.q=propagate%20your%20houseplants

I think you will have more success using the ''cane cutting'' method of propagating.

It could have been the lower temps and it could have been that the deep watering it got before you left caused root rot to set in. I would check for root rot (https://www.gardeningknowhow.com/plant-problems/disease/treating-root-rot-gardening-tips-for-housplants.htm) Regardless, it should recover if the stems are still alive. It may lose some (even all) its leaves, but will regrow from the stem.

Yes, pruning out the dead parts should help. For additional information, this article will provide tips for saving cold damaged plants: https://www.gardeningknowhow.com/plant-problems/environmental/tips-for-saving-cold-damaged-plants.htm

These plants cannot tolerate life outdoors year round unless you live in a suitable tropical-like climate. You can, however, allow them to spend summers outdoors. When you move it outside, make sure temps are above 50 degees at all times and protect it from direct sunlight shining on it.