is WordPress Secure for Online transactions

I’ve never built an e-commerce site using WordPress but today I have one of my clients require an online store for his business so I’ve make my research and find some negative points regarding using WordPress as E-Commerce Solution especially Safety issues! the question is WordPress Secure for Online transactions?

During my research I’ve found that core WordPress files are to some extent safe and the threat my come from four issues:

1) Used Plugins
2) Used Theme
3) Hosting
4) Database
I’m wondering how can customers data can be hacked in case I’m using gateways like authorize.net since all transactions occur there not on actually WordPress Site.

any recommendation for safe plugins, tweaks and tips.?

Thank you,