Help with date forecasting and week of the year

Hello Everyone,

I have an excel spread sheet that has column with dates in this format "1/1/2012", now each part our customer orders is assigned to different sorting managers. The data gets fed from a database in a report form that looks exactly like the excel sheet attached below. I am looking for a way I can forecast capacity of each sorting managers.

The best way of doing this I think would be to add the average number of duration for each services based on historical data and forecast when that service is going to be "completed". Now, I want to automatically group the date for each services if its "proposed" and based on the created date add the number of days it takes to finish the service. So, if the Created date is 4/15/2013, i need to automatically add 30 workdays to that service and forecast it will be done in "this date" to show how many services each sorting manager is working on currently and when are they going to available when we sign new customers. I need this to be dynamic in a way because on average we get about 4000-5000 services a week and it would be impossible to manually forecast. I have added a file with what the data looks like and what i want excel to do in the next sheet. I am looking for some help.

Thanks.