Hi. The truth is your options are a bit limited with BigCommerce when it comes to backing up, simply because they have never implemented a full backup feature, and you don't have as much control as you would with a self-hosted website. There are still something you can do to ensure you have product catalog data, theme files, order data etc., and I'll be happy to help you in this area.
Also, please take a quick look at my profile/feedback and you'll notice I'm a 100% trusted freelancer, a reputation built from perfect accuracy, attention to detail, excellent efficiency and great communication. I strongly believe I'm the perfect candidate for your job and you can be confident knowing you've hired a professional who delivers on-time.
Thank you for reading my proposal and I look forward to hearing back from you toward the start of a healthy working relationship. I'm from the Caribbean so there's no language barrier between us. Kind Regards, Kenny.