I have 6 Years of Experience in Web Development using PHP, ASP.Net, C#, SQL Server, VB.Net, Mysql, Wordpress, Bootstrap, HTML-5, CSS-3, Jquery and may more technologies.
I have reviewed your requirement and seems that you should go with ASP.Net because you have huge user flow and PHP with MysQL will get slow. And security wise also ASP.Net with SQL server is better . I already developed ERP system in ASP.Net which is used by Shree Tirupati Courier, Shree Anajani Courier. Each company have more then 4000 branches across india.
Please let me know your suitable time for detail discussion. Looking forward your positive response.
Thanks