Seller - Supplier - Purchasing

Hello,
Firstly thanks alot , and health to hands if who created this system. its amazing fast and good.

i have some suggestions,
i think this system targetted only for sales
it would be much more better if there was;
Sellers (Suppliers)
Purchasing invoices
Payment Methods (Cheque Voucher, Bank, Credit Card, Cash)
Stock Quantity Management (Warehouse)