Developing a system for a company

Hi there. we will explain the current situation of our business and what we want to accomplish based on this project. We have two businesses which are separated from each other but the employees are the same. The first business is for selling some items and the second one is exchange. For the first business, we would like to have some kind of sale system. The system must include inventory, invoicing, customer contact, full report system, quotation, reminder to employee for following quotation, account payable and receivable (multi currencies must be supported) etc. For the second business, each employee sell or buy from customers so they need to fill in a form, which is included customer details, exchange rate, total amount, payment details, etc. Some times customers make partial payment which we want the case be open until they make the full payment. If the customers make the full payment employee submit the case and then employee in accounting department sees the case in his work que and book the item in accounting system. We want the system to be central so both businesses be able to use it, what it means is that after sale department (first business) invoiced customer that invoice will be sent to accounting department for booking. The system must have different users with different privileges (Managers must be able to over look everything). It is important that the system be expandable for future use ( for example customers have accounts and be able to use the system to fill in the form and follow the status of their orders) and be accessible from out side the company. By the way design is as important as functionality. we have one server (windows server 2008 R2), but we will add anything needed based on bidders' suggestions. We would appreciate if all the bidders let us know what kind of technology or method they want to use for developing the system. These are mentioned above are the least we need from the system so any suggestions for improving the system are welcome. Thanks Thanks