I am an old man actually selling on eBay,but trying to expand a little bit more our business,I already start with Shopify but I have no experience to select the right theme for 2000 items
I think you can use this theme for your business
If you have any question about this theme you can ask with that item author here
Hope will helpful for you.
you can check these Shopify Theme to choose one of them
You can import all items from ebay to your Shopify site. It is easier than to make new items from scratch.
You can check this collection https://themeforest.net/collections/6804804-the-best-shopify-themes