a) How could I display a horizontal scroll layout on a desktop-laptop and a vertical scroll on mobile-tablets? I have to create 2 shortcodes or there is settings for it?
b) If I create two shortcodes and index data on both will they use the same table or it will create a double data index?
c) Is the store-manager role possible to return results from SKU or EAN on search?
a) It is best to have two search bars for this purpose. It might be possible to achieve via custom codes, but that requires server side device detection, and that is not very reliable.
b) It will use the same table.
c) Do you mean only for users with the store manager role? Might be possible programmatically, but only when not using the index table engine.