I need a Inventory management service system SW

Dear
I am currently an ebay seller
Many young people in Korea hope to sell many Korean products on eBay.

So, they are taking a lot of lectures from global sellers academy.

However, they think it difficult to sell overseas and are also concerned about high shipping costs.

So I'm trying to do a business that helps prospective sellers on eBay.

Sellers in Korea can connect to eBay and listing for sale.
They think that it is difficult to solve international shipping problems and buyer's issues in the next step.
So I can help and support them in resolving the issues they have.

So I need a Inventory management service system

I would like to create and service a system that stores their (seller) products in my warehouse in the United States so that they can be shipped within the United States or to other countries according to the order, and also return goods to my warehouse.

1) Inventory management for each customer(seller)
- Inbound/Outbound
2) Barcode create for inbound products
- eBay's SKU automatically assigned
3) Assign ID to individual seller
4) Building a website to check the seller's inventory

If it has nothing to do with you, how can I
Can we build an inventory management service system?