Hi,
The most important thing when having an ecommerce website is the security of the credit card information of your customers. So the best security you can have on that is to use a payment gateway where the payment happens on the payment plateform website. That will guarantee the security of your customers credit card information.
Then, you should install as less extensions as possible. Each time you add a new extension on your website, it's a possible security risk added.
Other than that, I would recommend to have an automatic backup tool to backup your website everyday in case something goes wrong.
