3 to 5 pounds of sugar to bump up the ABV. I like my summer wines to be at about a 10% ABV. Test SG as you add sugar, being careful not to end up with too much water being added.
You can add only a portion of the F pack, but just understand that it will also have less of the flavoring, like the strawberry.
It is hard to add the F pack to taste, because W.E. has you add the F pack before all the less and sediment have been removed.
I guess you could hold off on adding the clarifier right after the F pack ---
Stabilize; add half the F pack, let it settle on its own for 24 hours, taste it for sweetness and repeat all after stabilize, until it tastes about right. The lees and sediment will still be in the wine, so that is why it needs to settle for about 24 hours.
Also understand you will be tasting green wine, but the more you sample green wine, the more you will become a good judge as to the final result... gotta get around the green taste.
Once it is about right, add the clarifier, stir it up really well, and let it clear.
I have never tried this myself, so move at your own risk.