I'm in the process of building my store and already have an ebay shop.
Quick run down:
I sell a particular silicone hose for a vehicle. Same product, different colours. For it be be in the correct category on ebay (motor vehicle parts) you can't list variations (colours) so I have say, 8 listings for the same product but in different colours. I know there's ways round this but you have to list it under a different ebay category which attracts a higher final fee %. Plus having 8 separate listings gives a higher chance of being seen as opposed to 1.
But anyway, On my Shopify store I have that single product with multiple choice (colours).
Are you able to sync/link the 8 separate ebay listings to the single product on Shopify so that it keeps track of the inventory?