Automated User Controlled Site to handled multiple functions

I am currently running an online business. I am looking to turn the entire function into an automated process. The processes I perform are: (1) I have multiple items that I list by excel file with isbn on a seller site. (2) I must make sure prices are changed to remain competitive to other sellers on the site. Handled using downloaded text file of all listings and current inventory numbers in tab delimited excel format. (3) Must maintain daily numbers available at 8 a day. (4)Must package and ship items using postage site software (available upon request) and purchase postage for each item delivery. (5) Must locate top selling items of the past 50 years to acquire and add to online inventory. Those are the functions I perform daily. I need a program or preferrably, a website set up that can utilize tools on different pages to perform these functions automatically. Needs to be able to put orders together with items and order numbers. I need the site to be able to store customer information so that sales campaigns can be started with customer database. I will give more detailed explanation to someone with interest and a competitive bid.