need to customize

Hi, I'm trying to start with salesforce, we are a company with 20 active staff We are a trading company so we both sale and purchase, We need to have our leads, contacts and accounts for our customers. We need to have a lead, account and contact, or at least only account and contact for each supplier to be added to the opportunity. Same goes for the products, as each product that we sell should be connected to an opportunity and at the same time, customer and supplier. Also we do have 4 different companies that need to issue PI and PO in different letterheads, we are using CONGA. Kindly let me know if there is any better suggestion. Kindly let me know if you have got any solution for it, Regards, Ibrahim