Yes, it is true that transplants are better in the fall as the plant is going into a dormant state and will not have as much of root shock. And propagation is quicker and will take better in the spring since the plant is sending out energy and growing.
However, since you are doing cuttings that you will be wintering over, I would go ahead and do the cuttings indoors now and let them develop a root system, put them into individual pots and let them go dormant in the pot this fall in a garage or basement. Then when spring arrives simply move them from the pot to their new home.
Technaflora products are really easy to use and they sell a kit with everything you would need including fertilizers through every stage of cuttings, vegetative, flower and fruiting. Seriously though whatever the instructions say, cut it in half and you will see NO side effects whatsoever! I have been using technaflora at half strength for years... full wont hurt, but half works the same from all I have noticed and my local garden shop guru suggested it in the first place.
Technaflora Plant Products - Product List
These kits are less than 30 dollars and last a LONG time... especially when you cut the recipe in half LOL
I would also suggest you get a cheap PH test kit and adjust your PH of the water you are using to fertilize/water your plants to around 6 as that is the PH that facilitates plants to uptake the most nutrients for maximum benefit of the plant.
I have worked in greenhouses, tree farms and managed a nursery or two... but only do it as a hobby anymore
