Seperate discount on total for customers

[linuxnewbie]

Good day, could you pls advice what contribution allows to edit a given order and apply a certain discount on the total for example 20% for different clients for example I can edit order 1,2 and 3 and apply 10% for 1 - 20% for the 2nd and 5% for the 3rd and the total will be updated accordingly.

 

another question please:

 

I found lot of report addons for another issue but none is giving me what I really need, what I need exactly is a products dropdown + date range, once selected I would like to know who bought this product within that date range as well as the quantity.

 

Thanks a lot in advance for your kind assistance