Hey Dan!
Nicholas here, a Shopify Guru.
Sounds like you need an app such Multi Vendor Marketplace. I've included a link to it below, so you can check it out.
It ticks many of the boxes you described:
- Admin can add new sellers through CSV file
- Admin can set global commission for all the sellers & can also set separate commission for individual seller.
- Site can be marketed
- Email notifications sent to customers as normal, also the Admin can send reminder to the vendor for order fulfillment & an automatic mail will be sent to the vendor.
- Sellers can easily manage the orders through the 'orders' from the seller account. From here, seller can view all the orders placed and can check the status.
Check out the link below for the full list of features!
Cheers,
Nicholas,
Shopify Guru
Multi-Vendor Marketplace app: https://apps.shopify.com/multi-vendor-marketplace