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The dieffenbachia may bloom with a flower that looks much like a calla lily. The problem is that the plant will usually die once it is finished blooming. However, by the time a dieffenbachia is ready to bloom, it will almost always have new side shoots growing from it, which you can take to grow a new plant. Keep in mind that flowering is also a rare event when grown as houseplants, so if you get one to bloom, consider yourself lucky!

It sounds like mealy bugs, though it could be some other type of pest. Nonetheless, it can be treated with neem oil. Here is more information: https://www.gardeningknowhow.com/plant-problems/pests/mealybugs-white-residue-on-plants-leaves.htm
https://www.gardeningknowhow.com/plant-problems/pests/pesticides/neem-oil-uses.htm

It is not as successful as rooting in water, but yes you can do this and have a pretty high chance of the cutting rooting successfully.

Iwould go to the website listed below. The site goes into detail about the plant

http://houseplants-care.blogspot.com/2006/08/dieffenbachia-dumb-cane-plant-care.html

The lower leaves of cuttings commonly yellow and drop off. This is because when the branch is separated from the rest of the plant, it no longer has water flowing into it through the plant's vascular system. The plant's response to no water is to pull nutrients out of the leaf - you see this as yellowing; pull water out of the leaf - wilting; then let the leaf go - dropping. That's why when you make cuttings, you generally pull off all but 2 or 3 leaves. Deiffenbachia is a little different, in that it roots so easily, people commonly just cut the stem into pieces and stick them into the soil. You should soon be the parent of bouncing baby dieff.