First thing that platform should I choose? I believe the simplest way to build a webshop is to use a CMS system. Systems are systems that are popular and well-tested. And these systems are simple to customize and simple to use. I advise you to choose WordPress. Why? So I will use any CMS system easily, I'm a software programmer, but my clients can't use most of the CMS systems. My experience is my clients can learn WordPress in a brief time and it can be used by them without my aid. And you will see at the end of the article.
In my view, the best way to ensure your WordPress security is via the use of a fix malware problems free backup plugin. This is a relatively inexpensive, easy and elegant to use way to be certain your site YOURURL.com is accessible to you.
Use strong passwords - Do your best to use a password, alpha-numeric. Easy to remember passwords are also easy to guess!
Yes, you need to do regular backups of your website. I recommend at least a weekly database backup and a monthly "full" backup. More, if at all possible. Definitely more if you make regular additions and changes to your website. If you have a community of people that are in there all the time, or make changes multiple times every day, a backup should be a minimum.
You can get an SSL Encyption Security for your WordPress blogs. The SSL Security makes encrypted and secure communications with your site. So that all transactions are listed, you may even keep history of communication and the all of the cookies. Be certain all your blogs get SSL security for protection.
Software: If you have installed scripts search Google for'wordpress security'. You'll get many tips on how to create your WP blog protected.