I have some experience with Kombucha so I thought I'd share my two-bits here.
First off - if you don't have a previous batch of Kombucha to start your next batch with (if, for example, this is your very first batch), you can use vinegar in place of the Kombucha. Especially if you are hydrating a dried scoby, as you won't be drinking this first batch anyway.
As for the sugar content - as previously mentioned, the bacteria in the scoby actually feed off this sugar and digest it, turning it into the beneficial probiotics that Kombucha is known for. The longer you ferment it for, the less sugar will be in the end product. If you are really concerned about sugar and want as little as possible in your Kombucha but don't like the taste of it when it gets to that stage, there are other ways you can use it, such as in salad dressing (in place of vinegar), or you can even mix it with water so it's not as strong.
If you have never had Kombucha before, I would recommend starting with about 1/4 cup per day. See how you feel and go from there. Some people do have reactions to it, especially if their gut bacteria is out of balance. But this can be avoided by starting slowly and increasing your daily amount bit by bit. I personally wouldn't drink more than about 1 cup per day.
If you still feel like you don't want any of the sugar in your diet but you do want the probiotic benefits - try making homemade traditional sauerkraut!
I hope that helps!