eCommerce Conversion Rate Optimization (CRO) Strategist. Founder and Strategist at eCommerce CRO agency Conversions Guaranteed, and host of The Conversions Podcast.
It really depends on what you need. The new BigCommerce templates are pretty modern looking and professional, and you should able to customize them to your needs.
This makes it impossible to put any tracking scripts on such a critical part of the conversion funnel. More importantly, this part of the funnel cannot be split tested.
I disagree. The best way to do it is just to get started doing testing, or hire a competent CRO firm to do it for you.
Your customers are not the same as your competitor's customers, or the customers of some case studies you've seen. Your results might vary (greatly).
The best case studies and tests which result in the greatest gain in the lifetime value of the customer are based on principles which improve the customer experience and allow you to connect and communicate with. Tactics might work in the short term, but over the longer term a strategic approach is best.