How to predict number of orders for coming weeks using previous week's data?
If you treat this problem as a time-series one, you will gain more information for predictions, because it includes several time related components, and you can customize your orders predictions based on week day(week-end, Black Fridays)

If you treat this problem as linear regression, you will only be able to predict for the one upcoming week and not several weeks in advance, as they will only depend on the latest record you gave as the predictor.

analytics vidhya has great tutorials on time-series problems.