Once you've staked the entire field, string all the stakes together so it makes it easier to line the field with the paint striper.
Line the field using a paint striper (Image 1). There a several available for purchase or rental. Roll it directly over your string and be sure to make your lines nice and straight.
Use the same athletic paint that you used to line the field to apply the numbers. We purchased 12" number stencils (Image 2) from a local sign shop, but you paint them free hand them if you prefer.