I can't imagine building a wheel for the first time without a nipple driver. It gets you real close to the best starting "tension" but at the start there is none. At this point though, I agree with above comments: back them all off. They could be a bit short so back them off so that each spoke has the same number of threads showing using only your fingers to turn the nipple. If some are still to tight, back them all of another couple of turns.