Let's see if we can give you a little more direction. My thoughts, just ferment it like you normally would, then taste it.
If you feel like it needs more tart flavor then add malic acid. Figure out how much you need by pulling a few measured samples and adding a measured amount of acid to each, starting with a small amount of acid and increasing the amount in each sample. When you find the sample you enjoy the taste of just scale up the amount of malic acid for the total amount of cider you have.
And as always, let us know of you've got questions!