I need a website built, with a database back-end and software plug-in built into it

I need a ecommerce website built (web designed and all), which will have a software plug-in, which allows customers to connect to other e-commerce sites and will have a database back- end for our staff to access our customers information This would contain a list of all our customers and their personal information(Name, telephone number, address, email etc), all the orders placed, and allow our staff to send out general emails to all customers and adjust our pricing information.