Hi dm
if you want medium to sweet wines then you either want sugar in your finished wine or artificial sweeteners.
I'm not a fan of artificial sweeteners, but if you are happy with them then that is the simple route. If not then you have 3 simple options for sugar in your end product ...
1/ use excess sugar, the yeast will not be able to tolerate the alcohol content and will die. Chances are your wine will be pretty strong unless you go rummaging about looking for a yeast with a lower alcohol tolerance than you would normally consider. Using a lot of sugar from the start is one cause of stuck fermentations, sauternes yeast is better at dealing with this situation than most yeasts ... not sure how much alcohol it can tolerate tho but my brews with sauternes have been neither unusually strong nor unusually weak. If you add your sugar gradually then you'll avoid the stuck fermentation problem and be able to choose from a wider selection of yeasts, but working out the ABV of your wine will be a little trickier!
2/ Stop the fermentation in its tracks when you reach the sweetness you want. You can do this by adding campden tablets/powder AND potassium sorbate.
3/ Add sugar to your finished wine when you serve it up.
I know its not an exact answer to your question about that specific kit, but i hope its helpful in as much as it means you can tailor your wines to your tastes.
