I did not try to use a non Shopify theme yet but I think it's impossible. And I would recommend you use this theme: Warehouse.
The Warehouse theme is a theme that is designed and supported by Maestrooo in order to display and promote a large catalog of products. It is a neat theme with the simple design to be flexibly applied to your Shopify eCommerce store. This theme can be personalized by adjusting the color, inserting images up to your wish. There are tons of features available on Warehouse for you to use, like the Stock Level Indicator, Live Search, Custom Promotion Tiles, and many more.
Plus, as it focuses on the user experience, Warehouse enables you to broaden your customer reach to platforms, such as social media and email, for example. As a consequence, you can save an amount of money and time from developing your theme from scratch. There are two different styles available on Warehouse, which are Metal and Wood for you to flexibly choose and capture your customer’s attention right at the moment they land on your store by using the product slide show.
Also, there are many Shopify experts and designers have tested and recommended theme to use for big Shopify stores. What is more, the Warehouse theme is absolutely a compatible theme with Shopify that allows you to access to all updates here from Shopify.
By the way, If you have any trouble while do your business on Shopify, Avada Commerce would be an useful website you should visit.
Hope it helps!
Nick here from Shopify. Great questions!
This is a decision that is completely up to you. I spoke to someone on our theme support team who said it was difficult to truly say if a theme like Wokiee is worth it or not as they don't have any experience with it. They wouldn't have knowledge in regards to their performance and could be perfect for your needs, but that is not for anyone else to decide but you. A lot of this comes down to the theme I and the level of support the development company who created it are willing to provide. Something to keep in mind is that any paid theme from third-party developer, even from the Shopify theme store is not supported by Shopify.
Regarding a theme in the Shopify store which is good for having a large catalog. You can see the full list of recommend themes for this here.
I hope this helps and answers your question. Let me know if you have any others!
All the best, Nick