Hi there.
We are a reputed software company and have 50+ employees with offices in US, UK and India. We have read your requirements and are keen to discuss things further.
We have developed many b2b sites with extensive catalogs and other ecommerce features like cart, payment gateway integration, etc. All of them have complete admin panels. We are well equiped to understand and handle your requirements. A have posted a few reference url as pm.
Thanks.