I can provide you with a monthly forecast that identifies what should be purchased based on forecasted demand to include factors such as sales, supplier's capacity and on time delivery, shipping lead time (boat, train, truck), internal processing delays (if applicable), and desired safety stock levels. I would also suggest a review of the previous month's performance to forecast which would provide proactive insight if demand has changed and the forecast should be revised. This review should be done with Sales, Supply Chain, and Operations (SIOP).
My background is in Supply Chain and Production and Operations Management at a $150m company, the majority of which is in oil and gas valve manufacturing. It is critical to the success of the business that forecasting be as accurate as possible, including all relevant factors. The Newsboy method is a good strategy but there are some additional factors to consider.