Start by checking if you have enough steerer to add some spacers under the stem you have. You don't want the steerer top to be more than halfway down the clamp.. Bringing them up a little also shortens the effective reach more than you imagine it will. You can shift the saddle forward or back to experiment with the reach some. Once you settle, you can measure the reach from saddle to bars, and find the difference between that and you knee over peddle position to get your stem length. I like the "7" stems from Velo Orange, they gives lots of room for adjustment, and don't leave your bike with the embarasing erection up front. Swapping them out to experiment gets expensive, and your comfort with the road position will build over time.