Hey there!
Your requirement is pretty clear to me.
I'll just write it down in my own words:
1. You need an order page, where customers can select the items and the quantity, and then add the Customer information
2. A payment gateway to make an online payment.
3. Sellers should be able to update the items, prices, and available quantities. And customize the look n feel of the page as per their brand.
Here's my solution:
1. I will create a Content Management System for the sellers. They can create their own account, add items, add prices, update branding images, etc.
2. Once they add their items, the one-page sales URL will be updated with the item information. This one-page sales URL can be shared to take orders.
3. When the customer comes on the one-page sales URL, they will be able to select the product and the qty, update their info, and pay online.
4. As soon as the payment is done, the respective seller will be notified via email. An email will also be sent to the customer.
5. In the CMS, we will also create a dashboard, that will show the number of sales per item, and the revenue generated. Which of course could be downloaded as an Excel or CSV.
The way I work:
1. I'll send you a Functional BluePrint that will have all the functionalities of the entire development, and you have to sign that off.
2. After that, I will start the development. No changes are allowed once the design's set
I can deliver this in 14 days.
Let me know what you think.
Best,
Debarshi