Hello there!
So seeing your question, we could figure out that you are currently troubleshooting syncing, inventory on Etsy and Shopify simultaneously.
We want to suggest a simple way out for this problem. You can opt for Etsy Marketplace Integration App.
There are multiple advantages that you get that will help you set up your store smoothly :
1)Inventory Sync
As you stated, you have an extensive collection, so instead of uploading inventories separately on both the platforms, i.e., Shopify and Etsy, this app will help you list all your products in one go with a supportive feature of inventory sync.
2)Manage orders
This app will help in managing orders, which can easily manage orders and ship the in-stock products.
3)Deleting products, made easy
Along With features like bulk upload, you can quickly delete your products. The products are out of stock or are no longer being sold in your store.
4)Multi Linguistic and Multi-Currency feature
With upgrading stores, global reach is also the goal for every seller, and to suffice these criteria, Etsy Marketplace Integration App fulfills the quotient to be multilingual.
The Multi-Currency feature is also available for smooth shipping globally.
5)Last but not least, All this and many more with 7days free trial!
We hope our answer helps you well.
Have a good day.